How can Creating a Healing Environment help you? What the research says

Creating a Healing Environment can be powerful for your health and wellness, both in creating healing spaces and in minimizing exposures which may impair your healing.

How can Creating a Healing Environment help you? What the research says

Many types of exposures can affect your body terrainthe internal conditions of your body, including nutritional status, fitness, blood sugar balance, hormone balance, inflammation and more, your experience of side effects and symptoms, and your cancer risk. Some exposures are helpful, but others may be harmful. We summarize the evidence of exposures with the strongest evidence and also those that are common exposures.

For suggestions on increasing beneficial exposures and reducing harmful ones, see Making changes in your environment ›

We summarize the clinical evidence for each medical benefit here. We begin with our assessment of the strength of evidence within each category, followed by a brief summary of individual studies or reviews of several studies. In assessing the strength of evidence, we consider the study design, number of participants, and the size of the treatment effect (how much outcomes changed with treatment).

To see more details, click the plus sign to the right of any section.

Our assessments of evidence for each medical benefit fall into one of these categories:

Strong evidence: consistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results
Good evidence: significant effects in one large or several mid-sized and well-designed clinical studies ( randomized controlled trialsa study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects with an appropriate placebo or other strong comparison control or observational studies that control for confounds)
Modest evidence: significant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies), or several small studies aggregated into a meta-analysis
Preliminary evidence: significant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect
Weak evidence: one or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects
Insufficient evidence: preclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example)

Learn more about how we research and rate therapies and practices in How We Rate Therapies ›

Exposures to nature

Exposures to nature can take several forms. While full immersion in a natural setting such as a forest is ideal, some benefits are found with exposure only to visual aspects of nature from indoors or to nature-based sounds.

Details of the research are listed in Time in Nature or Forest Bathing. Here we present only the summaries of the evidence.

Therapies

Time in Nature or Forest Bathing

Optimizing your body terrain

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of higher immune activation among adults and/or children with greater exposure to natural environments

Preliminary evidence of less inflammation among people ranging from healthy young adults to elderly adults with chronic obstructive pulmonary disease (COPD) or hypertension participating in forest bathing

Preliminary evidence of health-promoting changes in skin and gut microbiota among urban daycare children with greater exposure to nature

Managing side effects and promoting wellness

Preliminary evidence of less anxiety among people with cancer in an educational facility with outlooks on natural scenery

Preliminary evidence of better wellness and spiritual sense among people spending time in nature or listening to nature sounds

Weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of better sleep efficiency and sleep time among people with gastrointestinal tract cancer participating in forest therapy

Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of benefit not specific to people with cancer

Modest evidence of lower anxiety among people participating in forest bathing or spending time in a forest
Modest evidence of less anxiety and agitation among people without cancer in critical care listening to recordings of nature-based sounds
Modest evidence of lower blood pressure or heart rate among people with more exposure to nature
Modest evidence of better cognitive performance among people listening to nature-based sounds
Modest evidence of better mood among people listening to nature-based sounds
Modest evidence of less pain among people listening to recordings of nature-based sounds
Modest evidence of better reported health and well-being among people with exposure to nature
Modest evidence of lower risk of stress-related disorders among people with dense vegetation near their residences
Modest evidence of less stress and annoyance among people listening to nature-based sounds

Reducing cancer risk

Modest evidence of lower cancer mortality over 8 years among women living near higher levels of vegetation

Modest evidence of lower risk of breast cancer among people living in urban areas close to green space

Modest evidence of lower risk of childhood leukemia among children living in a large urban area within 250 m of an urban parks or urban wooded areas

Modest evidence of lower risk of prostate cancer among people with higher levels of residential greenness

Exposures to light and other radiation

Bright Light

Bright light during daytime hours comes naturally from the sun. Light from sources such as indoor lighting can also produce a similar light spectrum. Although bright light in daytime can improve sleep-wake rhythms, bright light—and especially blue-spectrum light—in the evening can interfere with your natural melatonin production. Higher concentrations of melatonin promote sleep, so bright light should be limited before sleep time.

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of improved sleep efficiency among fatigued people with cancer exposed to bright white light in the morning

Preliminary evidence of better mood, less fatigue or sleepiness, and less sleep disruption among people exposed to bright or blue-enriched light during waking hours and not during sleep hours

Optimizing your body terrain

Modest evidence of better balance of hormones related to sleep (melatonin) and wakefulness (cortisol) among people exposed to bright or blue-enriched light during the day and not in the evening

Higher saliva cortisol concentration among healthy males after bright light exposure in the morning compared to dim light, and similar findings with blue light compared to red light, in mid-sized¹Petrowski K, Buehrer S, Niedling M, Schmalbach B. The effects of light exposure on the cortisol stress response in human males. Stress. 2021 Jan;24(1):29-35. and small²Petrowski K, Bührer S, Albus C, Schmalbach B. Increase in cortisol concentration due to standardized bright and blue light exposure on saliva cortisol in the morning following sleep laboratory. Stress. 2021 May;24(3):331-337. RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects
Greater suppression of melatonin among healthy volunteers exposed to blue-enriched light compared to standard light in a small controlled triala study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial³Hanifin JP, Lockley SW et al. Randomized trial of polychromatic blue-enriched light for circadian phase shifting, melatonin suppression, and alerting responses. Physiology & Behavior. 2019 Jan 1;198:57-66.
Higher melatonin levels (less suppression) and earlier melatonin onset among patients in a psychiatric hospital unit exposed to a blue-depleted light environment from 6:30pm to 7:00am compared to standard lighting in a small RCT⁴Vethe D, Scott J et al. The evening light environment in hospitals can be designed to produce less disruptive effects on the circadian system and improve sleep. Sleep. 2021 Mar 12;44(3):zsaa194.
Increases in melatonin levels among stroke patients in rehabilitation facilities exposed during the day to artificial light imitating daylight compared to standard indoor lighting in a small RCT⁵West AS, Sennels HP et al. The effects of naturalistic light on diurnal plasma melatonin and serum cortisol levels in stroke patients during admission for rehabilitation: a randomized controlled trial. International Journal of Medical Sciences. 2019 Jan 1;16(1):125-134.
Lower melatonin levels (lower incidence of melatonin concentrations of 2 pg/ml or higher) without a clear statement of statistical significance among healthy male athletes exposed to either bright light or blue light late in the day compared to typical light exposure in a small RCT⁶Knaier R, Schäfer J et al. Effects of bright and blue light on acoustic reaction time and maximum handgrip strength in male athletes: a randomized controlled trial. European Journal of Applied Physiology. 2017 Aug;117(8):1689-1696.

Managing side effects and promoting wellness

Sleep disruption: preliminary evidence of improved sleep efficiencythe ratio of total sleep time to time in bed among fatigued people with cancer exposed to bright white light in the morning

Greater improvement in sleep efficiency, but not for sleep quality or other sleep parameters, among fatigued adults with cancer exposed to bright white light for 30 minutes every morning for 4 weeks compared to those exposed to dim red light for the same duration in a small RCT⁷Wu LM, Amidi A et al. The effect of systematic light exposure on sleep in a mixed group of fatigued cancer survivors. Journal of Clinical Sleep Medicine. 2018 Jan 15;14(1):31-39.

Fatigue or sleepiness

Preliminary evidence of better subjective alertness among healthy volunteers exposed to blue-enriched light

Preliminary evidence of less subjective sleepiness among night-shift workers exposed to blue-enriched white light during the nighttime

Better subjective alertness among healthy volunteers exposed to blue-enriched light compared to standard light in a small controlled trial⁸Hanifin JP, Lockley SW et al. Randomized trial of polychromatic blue-enriched light for circadian phase shifting, melatonin suppression, and alerting responses. Physiology & Behavior. 2019 Jan 1;198:57-66.
Less subjective sleepiness among night-shift workers exposed to blue-enriched white light during the nighttime compared to standard white light in a small RCT⁹Sletten TL, Ftouni S et al. Randomised controlled trial of the efficacy of a blue-enriched light intervention to improve alertness and performance in night shift workers. Occupational and Environmental Medicine. 2017 Nov;74(11):792-801.

Sleep disruption: preliminary evidence of less sleep disruption among people exposed to blue-depleted light during the evening and night

Slightly longer sleep times among patients in a psychiatric hospital unit exposed to a blue-depleted light environment from 6:30pm to 7:00am compared to standard lighting in a small RCT¹⁰Vethe D, Scott J et al. The evening light environment in hospitals can be designed to produce less disruptive effects on the circadian system and improve sleep. Sleep. 2021 Mar 12;44(3):zsaa194.

Symptoms not specific to cancer

Depression or mood: preliminary evidence of less depressed mood among women with moderate-to-severe premenstrual syndrome / premenstrual dysphoric disorder not using hormonal contraceptives treated with morning light therapy high in bright and blue light

Less depressed mood (negative affect) among women with moderate-to-severe premenstrual syndrome / premenstrual dysphoric disorder, but only those not using hormonal contraceptives, treated with morning light therapy high in bright and blue light compared to a sham session of more typical light in a small RCT;¹¹Aan Het Rot M, Miloserdov K, Buijze ALF, Meesters Y, Gordijn MCM. Premenstrual mood and empathy after a single light therapy session. Psychiatry Research. 2017 Oct;256:212-218. our note: the lack of effect among women using hormone contraceptives indicates this effect may be related to hormone balance

Light exposure in combination with other therapies

Higher measures of overall mood, self-esteem, and general sense of well-being and fewer symptoms on two measures of depression among women with symptoms of mild to moderate depression not taking any mood-altering medication and treated with a brisk 20-minute outdoor walk at target heart rate of 60% of maximum heart rate, increased light exposure throughout the day, and a vitamin regimen of 50 mg vitamin B1 (thiamine), 50 mg vitamin B6 (pyroxidine), 50 mg vitamin B2 (riboflavin), 400 mcg folic acid, 200 mcg selenium, and 400 IU vitamin D compared to a placebo vitamin in a mid-sized RCT¹²Brown MA, Goldstein-Shirley J, Robinson J, Casey S. The effects of a multi-modal intervention trial of light, exercise, and vitamins on women’s mood. Women Health. 2001;34(3):93-112.

Reducing cancer risk

Good evidence of lower risk of lymphoma, with some differences among subtypes, among people with higher exposure to ambient sunlight

Lower risk of both Hodgkin lymphoma and non-Hodgkin lymphoma, including most subtypes, among people with higher personal exposure to ambient sunlight at residence compared to lower exposures in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 26 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹³Kim HB, Kim JH. Sunlight exposure in association with risk of lymphoid malignancy: a meta-analysis of observational studies. Cancer Causes and Control. 2021 May;32(5):441-457.

Electronic devices/blue light

Electronic devices such as mobile phones, televisions, or computer screens typically emit light in the blue section of the light spectrum. The effects of these devices on sleep are thought to be related to exposure to their blue light. Many newer devices have options to switch to more yellow or amber light in the evening. Use of electronics can also increase exposure to electromagnetic fields (EMFs) such as wi-fi. EMFs are considered separately below.

Symptoms not related to cancer

Preliminary evidence of less confusion-bewilderment but more errors on tasks among healthy adults using conventional LED (blue light) smartphones before bedtime

Preliminary evidence of more fatigue among young adults exposed to blue light at night (using a mobile phone after going to bed)

Preliminary evidence of some worse indicators of sleep quality among children and adults using electronic devices near bedtime or after going to bed, but no negative effects for adults using electronic devices for 2 hours at night following exposure to bright light for 6.5 hours earlier in the day

Cognitive difficulties: preliminary evidence of less confusion-bewilderment but more errors on tasks among healthy adults using conventional LED (blue light) smartphones before bedtime

Less confusion-bewilderment but more errors on tasks among healthy adults using conventional LED (blue light) smartphones for 2½ hours before bedtime compared to suppressed blue light phones in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁴Heo JY, Kim K et al. Effects of smartphone use with and without blue light at night in healthy adults: a randomized, double-blind, cross-over, placebo-controlled comparison. Journal of Psychiatric Research. 2017 Apr;87:61-70.

Fatigue: preliminary evidence of more fatigue among young adults using a mobile phone after going to bed

More self-reported fatigue and later rise time among people aged 18-41 using a mobile phone after going to bed compared to no use in a mid-size observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁵Exelmans L, Van den Bulck J. Bedtime mobile phone use and sleep in adults. Social Science & Medicine. 2016 Jan;148:93-101.

Sleep disturbance: preliminary evidence of some worse indicators of sleep quality among children and adults using electronic devices near bedtime or after going to bed, but no negative effects for adults using electronic devices for 2 hours at night following exposure to bright light for 6.5 hours earlier in the day

About double the likelihood of inadequate sleep quantity and excessive daytime sleepiness and 46% higher likelihood of poor sleep quality among children aged 6 to 19 using portable media devices such as tablets or cell phones near bedtime compared with those not using devices near bedtime in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 11 controlled trialsa study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial, most of low quality¹⁶Carter B, Rees P, Hale L, Bhattacharjee D, Paradkar MS. A meta-analysis of the effect of media devices on sleep outcomes. JAMA Pediatrics. 2016 Dec 1;170(12):1202-1208.
Delayed onset and reduced production of melatonin during sleep, longer time to fall asleep, less REM sleep, decreased sleepiness an hour before bedtime, and impaired morning alertness, but no difference in total sleep time, sleep efficiency, or the duration of non-REM sleep, among healthy young adults using an e-reader for 4 hours before bedtime compared with those reading a print book for the same duration in a small RCT¹⁷Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences of the USA. 2015 Jan 27;112(4):1232-7.
No difference in sleepiness, sleep quantity or quality, or pre-sleep melatonin levels among healthy adults reading a book on either a tablet or on paper for 2 hours in the evening following constant exposure to indoor bright light for 6.5 hours in a small RCT¹⁸Rångtell FH, Ekstrand E et al. Two hours of evening reading on a self-luminous tablet vs. reading a physical book does not alter sleep after daytime bright light exposure. Sleep Medicine. 2016 Jul;23:111-118.
Worse self-reported sleep quality, time to fall asleep (latency), sleep efficiencythe ratio of total sleep time to time in bed, and disturbance and worse insomnia symptoms among people aged 18-94, and shorter self-reported sleep duration and earlier rise time among older phone users, using a mobile phone after going to bed compared to no use in a mid-size observational study¹⁹Exelmans L, Van den Bulck J. Bedtime mobile phone use and sleep in adults. Social Science & Medicine. 2016 Jan;148:93-101.
Less sleepiness among healthy adults after using conventional LED (blue light) smartphones for 2½ hours before bedtime compared to suppressed blue light phones in a small RCT²⁰Heo JY, Kim K et al. Effects of smartphone use with and without blue light at night in healthy adults: a randomized, double-blind, cross-over, placebo-controlled comparison. Journal of Psychiatric Research. 2017 Apr;87:61-70.

Electromagnetic fields

Many kinds of electromagnetic fields are generated by electrical appliances and devices, communications equipment, and electrical wiring and transmission. Some people may be more sensitive than others to EMFs, experiencing symptoms such as headaches or sleep disruption.

Insufficient (conflicting) evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of effects from extremely low frequency electromagnetic fields (ELF-EMFs)—produced by power lines, electrical wiring, and electrical equipment—on hormone levels related to sleep

Preliminary evidence of shorter time to fall asleep with exposure to signals used in mobile radio and two-way transceivers (TETRA)―used primarily in emergency communications systems―or in mobile communications systems (GSM900 EMF)

Insufficient (conflicting) evidence of effects on sleep from exposure to wi-fi or cellular signals

Your body terrain

Hormone imbalance: insufficient (conflicting) evidence of effects from extremely low frequency electromagnetic fields (ELF-EMFs)—produced by power lines, electrical wiring, and electrical equipment—on hormone levels related to sleep

Contradictory results across epidemiological, experimental, and animal studies of either lower melatonin or no evidence of an effect with exposure to ELF-EMFs without a clear understanding of what may be causing different findings in a review of observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods and experimental studies²¹Lewczuk B, Redlarski G et al. Influence of electric, magnetic, and electromagnetic fields on the circadian system: current stage of knowledge. BioMed Research International. 2014;2014:169459.
A weak trend toward a smaller increase of nighttime urinary melatonin metabolites, indicating lower melatonin production, after continuous ELF-MF exposure in early or late afternoon among healthy men, especially among men with lower excretion rates, compared to sham exposure in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects²²Crasson M, Beckers V, Pequeux C, Claustrat B, Legros JJ. Daytime 50 Hz magnetic field exposure and plasma melatonin and urinary 6-sulfatoxymelatonin concentration profiles in humans. Journal of Pineal Research. 2001 Oct;31(3):234-41.
No changes in circulating hormones (melatonin, growth hormone, prolactin, testosterone, or cortisol) among healthy good sleepers exposee to a low frequency electromagnetic field such as from power lines, electrical wiring, and electrical appliances while sleeping compared with those sleeping without exposure in a small controlled triala study design in which people are assigned to either an experimental group or a control group to compare the outcomes from different treatment; assignment is not random, and so this is not as strong a study design as a randomized controlled trial, but still stronger than an uncontrolled trial²³Akerstedt T, Arnetz B, Ficca G, Paulsson LE, Kallner A. A 50-Hz electromagnetic field impairs sleep. Journal of Sleep Research. 1999 Mar;8(1):77-81.

Symptoms not specific to cancer

Sleep disruption

Insufficient (conflicting) evidence of effects on sleep from exposure to wi-fi or cellular signals

Shorter time to fall asleep (sleep latency) among both young and older men, and a decrease in arousals during REM (dream stage) sleep among older men exposed to terrestrial trunked radio (TETRA) signals compared to no exposure in a small RCT²⁴Eggert T, Dorn H, Sauter C, Schmid G, Danker-Hopfe H. RF-EMF exposure effects on sleep—age doesn’t matter in men! Environmental Research. 2020 Dec;191:110173.
Shorter sleep latency and fewer arousals among elderly men and women, with different patterns by gender, with exposure before and during sleep to either TETRA or GSM900 EMF exposures compared to no exposure in a small RCT²⁵Danker-Hopfe H, Dorn H, Sauter C, Schmid G, Eggert T. An experimental study on effects of radiofrequency electromagnetic fields on sleep in healthy elderly males and females: gender matters! Environmental Research. 2020 Apr;183:109181.
No evidence of an effect on measures of sleep among healthy young men with whole-night wi-fi exposure compared to no exposure in a small RCT²⁶Danker-Hopfe H, Bueno-Lopez A et al. Spending the night next to a router—results from the first human experimental study investigating the impact of Wi-Fi exposure on sleep. International Journal of Hygiene and Environmental Health. 2020 Jul;228:113550.
No evidence of an effect on reported sleep quality or sleep stages in electroencephalogram architecture among young people exposed to electromagnetic fields emitted by 3G mobile phones compared to no exposure in a small RCT²⁷Lowden A, Nagai R, Åkerstedt T, Hansson Mild K, Hillert L. Effects of evening exposure to electromagnetic fields emitted by 3G mobile phones on health and night sleep EEG architecture. Journal of Sleep Research. 2019 Aug;28(4):e12813.
Increase of stage R sleep (dream stage) sleep, but considerable variability on other measures of sleep among healthy young men exposed to electromagnetic fields from cellular devices compared to controls in a small RCT²⁸Danker-Hopfe H, Dorn H et al. Effects of mobile phone exposure (GSM 900 and WCDMA/UMTS) on polysomnography based sleep quality: an intra- and inter-individual perspective. Environmental Research. 2016 Feb;145:50-60.
Changes in brain waves during a light-sleep stage, but substantial differences across individuals, among healthy young men exposed to pulse-modulated radiofrequency electromagnetic fields (such as those from mobile phones) compared to controls in a small RCT²⁹Lustenberger C, Murbach M et al. Inter-individual and intra-individual variation of the effects of pulsed RF EMF exposure on the human sleep EEG. Bioelectromagnetics. 2015 Apr;36(3):169-77.
Changes in brain waves and less sleep-dependent performance improvement in a motor sequence task among men exposed to pulse-modulated radiofrequency electromagnetic fields compared to controls in a small RCT³⁰Lustenberger C, Murbach M et al. Stimulation of the brain with radiofrequency electromagnetic field pulses affects sleep-dependent performance improvement. Brain Stimulation. 2013 Sep;6(5):805-11.
Changes in 13 of 177 variables characterizing the initiation and maintenance of sleep, which the researchers concluded did not indicate “a negative impact on sleep architecture”, among healthy young men exposed to electromagnetic fields from cellular devices compared to sham in a small RCT³¹Danker-Hopfe H, Dorn H, Bahr A, Anderer P, Sauter C. Effects of electromagnetic fields emitted by mobile phones (GSM 900 and WCDMA/UMTS) on the macrostructure of sleep. Journal of Sleep Research. 2011 Mar;20(1 Pt 1):73-81.
No evidence of an effect on subjective and objective measures of sleep among people exposed to mobile phone base station signals compared to sham in a mid-sized observational study³²Danker-Hopfe H, Dorn H, Bornkessel C, Sauter C. Do mobile phone base stations affect sleep of residents? Results from an experimental double-blind sham-controlled field study. American Journal of Human Biology. 2010 Sep-Oct;22(5):613-8.
Reduced total sleep time, sleep efficiency, and slow wave sleep among healthy good sleepers exposee to a low frequency electromagnetic field (50 Hz/1 mu Tesla electrical field) similar to fields from power lines, electrical wiring, and electrical appliances during sleep compared with those sleeping without exposure in a small controlled trial³³Akerstedt T, Arnetz B, Ficca G, Paulsson LE, Kallner A. A 50-Hz electromagnetic field impairs sleep. Journal of Sleep Research. 1999 Mar;8(1):77-81.

Reducing cancer risk

The International Agency for Research on Cancer classifies radiofrequency electromagnetic fields as possibly carcinogenic to humans (Group 2B).³⁴IARC Monographs on the Identification of Carcinogenic Hazards to Humans. International Agency for Research on Cancer. Viewed April 8, 2023.

Ionizing radiation

Sources of ionizing radiation include heat or light from the sun, medical diagnostic scans such as x-rays and CT scans, and gamma rays from radioactive elements. The most common radioactive exposure for most people is radon gas. Most other exposures to radioactive materials come from the workplace, although releases from nuclear power plants or uranium mines may also expose people in the community.

Ionizing radiation is classified a Group 1 carcinogen—there is enough evidence to conclude that it can cause cancer in humans—by the International Agency for Research on Cancer. We draw from the IARC summary, which we consider strong evidence, and add more recent research to it.

Ionizing radiation as a whole

Modest evidence of slightly higher risk of solid cancers among adults exposed to low cumulative doses of ionizing radiation

Modest evidence of slightly higher risk of leukemia among adults exposed to low cumulative doses of ionizing radiation, but substantially higher risk (almost three times as high) of leukemia among children

Ionizing radiation from the sun or indoor tanning exposure

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of solid cancers other than melanoma and other skin cancer among people using indoor tanning devices

Modest evidence of lower risk of breast cancer among people getting sun exposure

Strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of higher risk of eye cancer (melanoma) among people exposed to UV-emitting tanning devices

Weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of a slightly higher risk of blood cancer among users of indoor tanning devices

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of lymphoma, with some differences among subtypes, among people with higher exposure to sunlight

Modest evidence of lower risk of Hodgkin lymphoma positive for Epstein-Barr virus among people with the highest ultraviolet radiation exposure

Good evidence of higher risk of melanoma and other skin cancer among people with higher exposures to the sun or to indoor tanning

Ionizing radiation from medical imaging such as x-rays

Strong evidence of higher risk of cancer, including secondary cancer, among people receiving radiation therapy

Strong evidence of higher risk of bladder cancer; brain cancer; female breast cancer; colon cancer; esophageal cancer; stomach cancer; various head, neck, and oral cancers; kidney cancer; leukemia; lung cancer; skin cancer (basal-cell carcinoma); bone cancer; or thyroid cancer among people exposed to x-rays or ionizing radiation from other medical imaging

Modest evidence of higher risk of rectal cancer among people with prostate cancer treated with radiotherapy

Ionizing radiation from radioactive materials

Strong evidence of higher risk of gallbladder cancer or liver cancer among people exposed to thorium

Strong evidence of higher risk of various head, neck, and oral cancers among people exposed to radium

Strong evidence of higher risk of leukemia among people exposed to thorium, phosphorus, or strontium

Strong evidence of higher risk of liver cancer, lung cancer, or bone cancer among people exposed to radon or plutonium

Strong evidence of higher risk of thyroid cancer among people exposed to radioiodines

Ionizing radiation as a whole

Modest evidence of slightly higher risk of solid cancers among adults exposed to low cumulative doses of ionizing radiation

Slightly higher risk of solid cancers among adults exposed to low cumulative doses (less than 100 mGy) of ionizing radiation compared to no exposure in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 13 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies with low risk of bias³⁵Hauptmann M, Daniels RD et al. Epidemiological studies of low-dose ionizing radiation and cancer: summary bias assessment and meta-analysis. Journal of the National Cancer Institute. Monographs. 2020 Jul 1;2020(56):188-200.

Leukemia: modest evidence of slightly higher risk of leukemia among adults exposed to low cumulative doses of ionizing radiation, but substantially higher risk (almost three times as high) of leukemia among children

Slightly higher risk of leukemia among adults exposed to low cumulative doses (less than 100 mGy) of ionizing radiation compared to no exposure in a meta-analysis of 14 observational studies with low risk of bias³⁶Hauptmann M, Daniels RD et al. Epidemiological studies of low-dose ionizing radiation and cancer: summary bias assessment and meta-analysis. Journal of the National Cancer Institute. Monographs. 2020 Jul 1;2020(56):188-200.
Substantially higher risk (almost three times as high) of leukemia among children exposed to low cumulative doses (less than 100 mGy) of ionizing radiation compared to no exposure in a meta-analysis of 6 observational studies with low risk of bias³⁷Hauptmann M, Daniels RD et al. Epidemiological studies of low-dose ionizing radiation and cancer: summary bias assessment and meta-analysis. Journal of the National Cancer Institute. Monographs. 2020 Jul 1;2020(56):188-200.

Ionizing radiation from the sun or indoor tanning exposure

Cancer as a whole: no evidence of an effect on risk of solid cancers other than skin cancer among people using indoor tanning devices in a combined analysis of studies

No evidence of an effect on risk of solid cancers other than skin cancer (non-cutaneous cancers) among people using indoor tanning devices compared to non-users in a meta-analysis of 7 observational studies; the researchers conclude that “indoor tanning does not protect against solid non-cutaneous cancers”³⁸O’Sullivan DE, Hillier TWR, Brenner DR, Peters CE, King WD. Indoor tanning and the risk of developing non-cutaneous cancers: a systematic review and meta-analysis. Cancer Causes and Control. 2018 Oct;29(10):937-950.

Breast cancer: modest evidence of lower risk of breast cancer among people getting sun exposure

16% lower risk of breast cancer among people spending 1 or more hours a day in the sun during summer months over a lifetime or usual adulthood compared with less than 1 hour a day, and lower risk of breast cancer at age 45 or older among people with sun exposure during adolescence, in a meta-analysis of 13 observational studies³⁹Hiller TWR, O’Sullivan DE, Brenner DR, Peters CE, King WD. Solar ultraviolet radiation and breast cancer risk: a systematic review and meta-analysis. Environmental Health Perspectives. 2020 Jan;128(1):16002.
30% lower risk of breast cancer among people with the highest exposure to solar ultraviolet radiation compared to the lowest in a meta-analysis of 6 observational studies⁴⁰Li Y, Ma L. Exposure to solar ultraviolet radiation and breast cancer risk: a dose-response meta-analysis. Medicine (Baltimore). 2020 Nov 6;99(45):e23105.

Head, neck, and oral cancer: strong evidence of a higher risk of eye cancer (melanoma) among people exposed to UV-emitting tanning devices

Higher risk of eye cancer (melanoma) among people exposed to UV-emitting tanning devices in a comprehensive review of evidence⁴¹El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Lymphoma and leukemia

Good evidence of lower risk of lymphoma, with some differences among subtypes, among people with higher exposure to sunlight

Modest evidence of lower risk of Hodgkin lymphoma positive for Epstein-Barr virus among people with the highest ultraviolet radiation exposure

Weak evidence of a slightly higher risk of blood cancer among users of indoor tanning devices

Lower risk of both Hodgkin lymphoma and non-Hodgkin lymphoma, including most subtypes, among people with higher personal exposure to sunlight compared to lower exposures, and higher numbers of sunburns and sunbaths showed a trend toward decreasing risk, in a very large meta-analysis of 26 observational studies⁴²Kim HB, Kim JH. Sunlight exposure in association with risk of lymphoid malignancy: a meta-analysis of observational studies. Cancer Causes and Control. 2021 May;32(5):441-457.
Lower risk of Hodgkin lymphoma positive for Epstein-Barr virus among people with the highest ultraviolet radiation exposure compared to the lowest in a meta-analysis of 4 observational studies⁴³Monnereau A, Glaser SL et al. Exposure to UV radiation and risk of Hodgkin lymphoma: a pooled analysis. Blood. 2013 Nov 14;122(20):3492-9.
A weak trend toward a slightly higher risk of blood cancers among users of indoor tanning devices compared to non-users in a meta-analysis of 7 observational studies⁴⁴O’Sullivan DE, Hillier TWR, Brenner DR, Peters CE, King WD. Indoor tanning and the risk of developing non-cutaneous cancers: a systematic review and meta-analysis. Cancer Causes and Control. 2018 Oct;29(10):937-950.

Melanoma and other skin cancer: strong evidence of higher risk of skin cancer among people with higher exposures to the sun or to indoor tanning

Higher risk of skin cancer (basal-cell carcinoma, squamous-cell carcinoma, and melanoma) among people exposed to solar radiation in a comprehensive review of evidence⁴⁵El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.
Higher risk of skin cancer (melanoma) among people exposed to UV-emitting tanning devices in a comprehensive review of evidence⁴⁶El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.
Higher risk of melanoma among people ever using indoor tanning compared with no indoor tanning in a very large meta-analysis of 31 observational studies of low to moderate quality⁴⁷Colantonio S, Bracken MB, Beecker J. The association of indoor tanning and melanoma in adults: systematic review and meta-analysis. Journal of the American Academy of Dermatology. 2014 May;70(5):847-57.e1-18.
67% higher risk of squamous cell carcinoma and 29% higher risk of basal cell carcinoma among people ever using indoor tanning compared with no indoor tanning in a meta-analysis of 12 observational studies⁴⁸Wehner MR, Shive ML et al. Indoor tanning and non-melanoma skin cancer: systematic review and meta-analysis. BMJ. 2012 Oct 2;345:e5909.
38% higher risk of melanoma, 39% higher risk of basal cell carcinoma and 49% higher risk of squamous cell carcinoma among people in Canada ever using indoor tanning compared with those who never used indoor tanning in a meta-analysis of observational studies and surveys⁴⁹O’Sullivan DE, Brenner DR et al; ComPARe Study Group. Indoor tanning and skin cancer in Canada: a meta-analysis and attributable burden estimation. Cancer Epidemiology. 2019 Apr;59:1-7.
Substantially higher risk of basal cell carcinoma among Caucasian people in Canada practicing adult sunbathing (82% higher risk) or experiencing adult sunburn (85% higher risk); risks of squamous cell carcinoma were 14% and 41% higher, respectively, in an analysis of prevalence estimates and survey data⁵⁰O’Sullivan DE, Brenner DR, Villeneuve PJ, Walter SD, Demers PA, Friedenreich CM, King WD; ComPARe Study Team. The current burden of non-melanoma skin cancer attributable to ultraviolet radiation and related risk behaviours in Canada. Cancer Causes and Control. 2021 Mar;32(3):279-290.
20% higher risk of any skin cancer among people in Europe ever using indoor tanning compared with no indoor tanning, with increasing risk with more use, in a meta-analysis of 27 studies⁵¹Boniol M, Autier P, Boyle P, Gandini S. Cutaneous melanoma attributable to sunbed use: systematic review and meta-analysis. BMJ. 2012 Jul 24;345:e4757.

Ionizing radiation from medical diagnostic and/or treatment imaging, such as x-rays

Cancer as a whole: strong evidence of higher risk of cancer, including secondary cancer, among people receiving radiation therapy

Higher risk of cancer among people receiving radiation therapy compared to no radiation therapy in combined very large meta-analyses of 21,⁵²Wallis CJ, Mahar AL et al. Second malignancies after radiotherapy for prostate cancer: systematic review and meta-analysis. British Medical Journal. 2016 Mar 2;352:i851. 23,⁵³Rombouts AJM, Hugen N et al. Does pelvic radiation increase rectal cancer incidence?—a systematic review and meta-analysis. Cancer Treatment Reviews. 2018 Jul;68:136-144. 13,⁵⁴Grantzau T, Overgaard J. Risk of second non-breast cancer after radiotherapy for breast cancer: a systematic review and meta-analysis of 762,468 patients. Radiotherapy and Oncology. 2015 Jan;114(1):56-65. 22,⁵⁵Grantzau T, Overgaard J. Risk of second non-breast cancer among patients treated with and without postoperative radiotherapy for primary breast cancer: a systematic review and meta-analysis of population-based studies including 522,739 patients. Radiotherapy and Oncology. 2016 Dec;121(3):402-413. 16,⁵⁶Zhu Z, Zhao S et al. Risk of secondary rectal cancer and colon cancer after radiotherapy for prostate cancer: a meta-analysis. International Journal of Colorectal Disease. 2018 Sep;33(9):1149-1158. and 26⁵⁷Doi K, Mieno MN, Shimada Y, Yonehara H, Yoshinaga S. Meta-analysis of second cancer risk after radiotherapy among childhood cancer survivors. Radiation Protection Dosimetry. 2011 Jul;146(1-3):263-7. observational studies, plus further very large individual observational studies⁵⁸Wu Y, Chong Y et al. Second primary malignancies associated with radiation therapy in cervical cancer patients diagnosed between 1975 and 2011: a population-based competing-risk study. Annals of Translational Medicine. 2021 Sep;9(17):1375; Rombouts AJM, Hugen N et al. Increased risk for second primary rectal cancer after pelvic radiation therapy. European Journal of Cancer. 2020 Jan;124:142-151; Mazonakis M, Kachris S, Damilakis J. Second cancer risk from radiation therapy for common solid tumors diagnosed in reproductive-aged females. Radiation Protection Dosimetry. 2018 Dec 1;182(2):208-214. although no increased risk in large observational studies of radiation therapy for rectal or endometrial cancer⁵⁹Wiltink LM, Nout RA et al. No increased risk of second cancer after radiotherapy in patients treated for rectal or endometrial cancer in the randomized TME, PORTEC-1, and PORTEC-2 trials. Journal of Clinical Oncology. 2015 May 20;33(15):1640-6. and lower risk after radiation therapy for lung cancer⁶⁰Han C, Wu Y et al. Long-term radiation therapy-related risk of second primary malignancies in patients with lung cancer. Journal of Thoracic Disease. 2021 Oct;13(10):5863-5874.

Bladder cancer: strong evidence of higher risk of bladder cancer among people exposed to x-rays

Higher risk of bladder cancer among people exposed to x-rays in a comprehensive review of evidence⁶¹El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Brain cancer: strong evidence of higher risk of brain cancer among people exposed to radiation from medical imaging and treatment devices, including x-rays

Higher risk of brain and central nervous system cancer among people exposed to x-rays in a comprehensive review of evidence⁶²El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.
Higher risk of brain cancer among people younger than 22 years exposed to ionizing radiation from medical imaging compared to other people in a meta-analysis of 24 observational studies⁶³Abalo KD, Rage E et al. Early life ionizing radiation exposure and cancer risks: systematic review and meta-analysis. Pediatric Radiology. 2021 Jan;51(1):45-56.
Slightly increased risk of meningioma among people exposed to dental bitewing X-rays, but no evidence of an effect of dental x-rays as a whole or full-mouth panorex x-rays compared to controls in a large meta-analysis of 7 observational studies⁶⁴Xu P, Luo H et al. Exposure to ionizing radiation during dental X-rays is not associated with risk of developing meningioma: a meta-analysis based on seven case-control studies. PLoS One. 2015 Feb 6;10(2):e0113210.
53% higher risk of meningioma among people with multiple (or repeated) exposures to dental X-rays compared to other people in a large meta-analysis of 8 observational studies⁶⁵Memon A, Rogers I, Paudyal P, Sundin J. Dental x-rays and the risk of thyroid cancer and meningioma: a systematic review and meta-analysis of current epidemiological evidence. Thyroid. 2019 Nov;29(11):1572-1593.
13% higher risk of meningioma among people exposed to dental ionizing radiation at diagnostic levels compared to no exposures in a meta-analysis of 6 observational studies⁶⁶Mupparapu M, Baddam VRR, Lingamaneni KP, Singer SR. Dental x-ray exposure is not associated with risk of meningioma: a 2019 meta-analysis. Quintessence International. 2019;50(10):822-829.

Breast cancer: strong evidence of higher risk of female breast cancer among people exposed to x-rays

Higher risk of female breast cancer among people exposed to x-rays in a comprehensive review of evidence⁶⁷El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Colorectal cancer

Strong evidence of higher risk of colon cancer among people exposed to x-rays

Modest evidence of higher risk of rectal cancer among people with prostate cancer treated with radiotherapy

Higher risk of colon cancer among people exposed to x-rays in a comprehensive review of evidence⁶⁸El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.
Higher risk of rectal cancer among people with prostate cancer treated with radiotherapy compared to those treated by non-radiotherapy treatments in a very large meta-analysis of 8 observational studies⁶⁹Nugent TS, Low EZ et al. Prostate radiotherapy and the risk of secondary rectal cancer-a meta-analysis. International Journal of Colorectal Disease. 2022 Feb;37(2):437-447.

Gastrointestinal cancer: strong evidence of higher risk of esophageal or stomach cancer among people exposed to x-rays

Higher risk of esophageal or stomach cancer among people exposed to x-rays in a comprehensive review of evidence⁷⁰El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Head, neck, and oral cancer: strong evidence of higher risk of various head, neck, and oral cancers among people exposed to x-rays

Higher risk of various head, neck, and oral cancers among people exposed to x-rays in a comprehensive review of evidence⁷¹El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Kidney cancer: strong evidence of higher risk of kidney cancer among people exposed to x-rays

Higher risk of kidney cancer among people exposed to x-rays in a comprehensive review of evidence⁷²El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Leukemia: strong evidence of higher risk of leukemia among people exposed to ionizing radiation from medical imaging

Higher risk of leukemia among people exposed to x-rays in a comprehensive review of evidence⁷³El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.
Higher risk of leukemia among people younger than 22 years exposed to ionizing radiation from medical imaging devices compared to other people in a meta-analysis of 24 observational studies⁷⁴Abalo KD, Rage E et al. Early life ionizing radiation exposure and cancer risks: systematic review and meta-analysis. Pediatric Radiology. 2021 Jan;51(1):45-56.

Lung cancer: strong evidence of higher risk of lung cancer among people exposed to x-rays

Higher risk of lung cancer among people exposed to x-rays in a comprehensive review of evidence⁷⁵El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Melanoma and other skin cancer: strong evidence of higher risk of skin cancer (basal-cell carcinoma) among people exposed to x-rays

Higher risk of skin cancer (basal-cell carcinoma) among people exposed to x-rays in a comprehensive review of evidence⁷⁶El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Sarcoma: strong evidence of higher risk of bone cancer among people exposed to x-rays

Higher risk of bone cancer among people exposed to x-rays in a comprehensive review of evidence⁷⁷El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Thyroid cancer: strong evidence of higher risk of thyroid cancer among people exposed to radiation from medical imaging or treatment devices

Higher risk of thyroid cancer among people exposed to x-rays in a comprehensive review of evidence⁷⁸El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.
Higher risk of thyroid cancer among people exposed to diagnostic x-rays such as CT scans or dental x-rays compared to other people in a meta-analysis of 9 observational studies⁷⁹Han MA, Kim JH. Diagnostic x-ray exposure and thyroid cancer risk: systematic review and meta-analysis. Thyroid. 2018 Feb;28(2):220-228.
87% higher risk of thyroid cancer among people with multiple (or repeated) exposures to dental x-rays compared to other people in a meta-analysis of 7 observational studies⁸⁰Memon A, Rogers I, Paudyal P, Sundin J. Dental x-rays and the risk of thyroid cancer and meningioma: a systematic review and meta-analysis of current epidemiological evidence. Thyroid. 2019 Nov;29(11):1572-1593.

Ionizing radiation from radioactive materials

Gastrointestinal cancer

Strong evidence of higher risk of liver cancer among people exposed to thorium or plutonium

Strong evidence of higher risk of gallbladder cancer among people exposed to thorium

Higher risk of liver cancer among people exposed to thorium or plutonium in a comprehensive review of evidence⁸¹El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.
Higher risk of gallbladder cancer among people exposed to thorium in a comprehensive review of evidence⁸²El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Head, neck, and oral cancer: strong evidence of higher risk of head, neck, and oral cancers among people exposed to radium

Higher risk of head, neck, and oral cancers among people exposed to radium in a comprehensive review of evidence⁸³El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Leukemia: strong evidence of higher risk of leukemia among people exposed to thorium, phosphorus, or strontium

Higher risk of leukemia among people exposed to thorium, phosphorus, or strontium in a comprehensive review of evidence⁸⁴El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Lung cancer: strong evidence of higher risk of lung cancer among people exposed to radon or plutonium

Higher risk of lung cancer among people exposed to radon or plutonium in a comprehensive review of evidence⁸⁵El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Sarcoma: strong evidence of higher risk of bone cancer among people exposed to radium or plutonium

Higher risk of bone cancer among people exposed to radium or plutonium in a comprehensive review of evidence⁸⁶El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Thyroid cancer: strong evidence of higher risk of thyroid cancer among people exposed to radioiodines

Higher risk of thyroid cancer among people exposed to radioiodines in a comprehensive review of evidence⁸⁷El Ghissassi F, Baan R et al; WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens—part D: radiation. Lancet Oncology. 2009 Aug;10(8):751-2.

Exposures to chemicals and other substances

Air pollution

Air pollution comes from many sources and can contain many chemicals. The evidence related to cancer focuses on the presence of tiny particulates (particulate matter, or PM) and nitrogen dioxide, common pollutants from vehicles and from industrial burning. Particulates can also come from wildfires, agriculture, mining, and other sources. Smoking tobacco and burning paraffin candles are main sources of indoor air particulates.

Cancer mortality

Modest evidence of a small increase in lung cancer mortality among people without cancer at baseline with higher exposures to nitrogen dioxide, a marker of traffic-related air pollution

Cancer risk

Modest evidence of a small increase in risk of brain cancer among people exposed to ultrafine particulate air pollution

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of higher risk of breast cancer among people living in areas with higher air pollution levels

Modest evidence of higher risk of mouth and throat cancer, nonmelanoma skin cancer, or prostate cancer among people living in areas with higher levels of particulate air pollution

Good evidence of higher risk of leukemia among people exposed to air pollutants

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of colorectal cancer among people living in areas with higher levels of particulate matter pollution

Cancer mortality

Cancer as a whole: modest evidence of a small increase in cancer mortality among people without cancer at baseline with higher exposures to particulate air pollutants

15% increased cancer mortality with each unit increase in PM2.5 (10 µg/m3) among people without cancer at baseline in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁸⁸Coleman NC, Burnett RT, et al. Cancer mortality risk, fine particulate air pollution, and smoking in a large, representative cohort of US adults. Cancer Causes & Control. 2020 Aug;31(8):767-776.

Bladder cancer: modest evidence of a small increase in bladder cancer mortality among people without cancer at baseline with higher exposures to particulate air pollutants

13% higher mortality from bladder cancer with each unit increase in PM2.5 (4.4 μg/m3), with similar increases for PM2.5 combined with nitrogen dioxide and/or ozone, among people without cancer at baseline in a very large observational study⁸⁹Turner MC, Krewski D et al. Ambient air pollution and cancer mortality in the Cancer Prevention Study II. Environmental Health Perspectives. 2017 Aug 21;125(8):087013.

Colorectal cancer: modest evidence of a small increase in colorectal cancer mortality among people without cancer at baseline with higher exposures to air pollutants

6% higher mortality from colorectal cancer with each unit increase in PM2.5 (4.4 μg/m3), with similar increases for PM2.5 combined with nitrogen dioxide and/or ozone, among people without cancer at baseline in a very large observational study⁹⁰Turner MC, Krewski D et al. Ambient air pollution and cancer mortality in the Cancer Prevention Study II. Environmental Health Perspectives. 2017 Aug 21;125(8):087013.

Kidney cancer: modest evidence of a small increase in kidney cancer mortality among people without cancer at baseline with higher exposures to particulate air pollutants

14% higher mortality from kidney cancer with each unit increase in PM2.5 (4.4 μg/m3), with similar increases for PM2.5 combined with nitrogen dioxide and/or ozone, among people without cancer at baseline in a very large observational study⁹¹Turner MC, Krewski D et al. Ambient air pollution and cancer mortality in the Cancer Prevention Study II. Environmental Health Perspectives. 2017 Aug 21;125(8):087013.

Lung cancer: modest evidence of a small increase in lung cancer mortality among people without cancer at baseline with higher exposures to nitrogen dioxide, a marker of traffic-related air pollution

8.3% higher mortality from lung cancer with each unit (10 ppb) increase in long-term exposure to nitrogen dioxide among adults without cancer at baseline in a large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of observational studies of moderate quality⁹²Stieb DM, Berjawi R et al. Systematic review and meta-analysis of cohort studies of long term outdoor nitrogen dioxide exposure and mortality. PLoS One. 2021 Feb 4;16(2):e0246451.

Cancer risk

Brain cancer: modest evidence of a small increase in risk of brain cancer among people exposed to ultrafine particulate air pollution

11% higher risk of brain tumors with each unit increase in ultrafine particle pollution (10,000/cm), but no change in risk with increases in PM2.5 or nitrogen oxide, among people without cancer at baseline in a very large observational study⁹³Weichenthal S, Olaniyan T et al. Within-city spatial variations in ambient ultrafine particle concentrations and incident brain tumors in adults. Epidemiology. 2020 Mar;31(2):177-183.

Breast cancer: good evidence of higher risk of breast cancer among people living in areas with higher air pollution levels

19% higher risk of breast cancer among people living in areas with higher levels of particulate matter pollution (PM10 of 10 μg/m3) in a very large observational study⁹⁴Datzmann T, Markevych I et al. Outdoor air pollution, green space, and cancer incidence in Saxony: a semi-individual cohort study. BMC Public Health. 2018 Jun 8;18(1):715.
13-17% higher risk of breast cancer with a 9.7ppb increase in nitrogen dioxide, a marker for traffic-related pollution, among premenopausal women, but no change in risk for menopausal women, in a very large observational study⁹⁵Goldberg MS, Villeneuve PJ et al. Associations between incident breast cancer and ambient concentrations of nitrogen dioxide from a national land use regression model in the Canadian National Breast Screening Study. Environment International. 2019 Dec;133(Pt B):105182.

Colorectal cancer: no evidence of an effect on risk of colorectal cancer among people living in areas with higher levels of particulate matter pollution

No evidence of an effect on risk of colorectal cancer among people living in areas with higher levels of particulate matter pollution (PM10 of 10 μg/m3) in a very large observational study⁹⁶Datzmann T, Markevych I et al. Outdoor air pollution, green space, and cancer incidence in Saxony: a semi-individual cohort study. BMC Public Health. 2018 Jun 8;18(1):715.

Head, neck, and oral cancer: modest evidence of higher risk of mouth and throat cancer among people living in areas with higher levels of particulate air pollution

53% higher risk of mouth and throat cancer among people living in areas with higher levels of particulate matter pollution (PM10 of 10 μg/m3) in a very large observational study⁹⁷Datzmann T, Markevych I et al. Outdoor air pollution, green space, and cancer incidence in Saxony: a semi-individual cohort study. BMC Public Health. 2018 Jun 8;18(1):715.

Leukemia: good evidence of higher risk of leukemia among people exposed to air pollutants

4% increased risk of leukemia among people with higher exposure to nitrogen dioxide in a meta-analysis of 20 observational studies of good quality⁹⁸Wei T, Jiao R et al. Exposure to outdoor air pollution at different periods and the risk of leukemia: a meta-analysis. Environmental Science and Pollution Research International. 2021 Jul;28(27):35376-35391.
30% higher risk of leukemia among people living within 5 kilometers (3 miles) of a refinery or manufacturer of commercial petrochemicals compared to other people in a meta-analysis of 16 observational studies of moderate quality⁹⁹Jephcote C, Brown D, Verbeek T, Mah A. A systematic review and meta-analysis of haematological malignancies in residents living near petrochemical facilities. Environmental Health. 2020 May 19;19(1):53.

Melanoma and other skin cancers: modest evidence of higher risk of nonmelanoma skin cancer among people living in areas with higher levels of particulate air pollution

52% higher risk of nonmelanoma skin cancer among people living in areas with higher levels of particulate matter pollution (PM10 of 10 μg/m3) in a very large observational study¹⁰⁰Datzmann T, Markevych I et al. Outdoor air pollution, green space, and cancer incidence in Saxony: a semi-individual cohort study. BMC Public Health. 2018 Jun 8;18(1):715.

Prostate cancer: modest evidence of higher risk of prostate cancer among people living in areas with higher levels of particulate matter pollution

23% higher risk of prostate cancer among people living in areas with higher levels of particulate matter pollution (PM10 of 10 μg/m3) in a very large observational study¹⁰¹Datzmann T, Markevych I et al. Outdoor air pollution, green space, and cancer incidence in Saxony: a semi-individual cohort study. BMC Public Health. 2018 Jun 8;18(1):715.

Arsenic and other heavy metals

Arsenic occurs naturally in soil and groundwater, but it also is deposited as a result of mining, smelting, or industrial use. Tobacco smoke also contains arsenic. Arsenic is classified a Group 1 carcinogen—there is enough evidence to conclude that it can cause cancer in humans—by the International Agency for Research on Cancer (IARC). We draw from the IARC summary, which we consider strong evidence, and add more recent research to it.

Arsenic is one of many heavy metals. While some heavy metals are essential to plant growth, others are not, such as lead, cadmium, chromium, mercury, and aluminum. All are toxic.

Strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of higher risk of bladder cancer among people drinking water with higher levels of arsenic

Modest evidence of higher liver cancer mortalitydeath, or the death rate in a population; cancer studies often report all-cause mortality (death from any cause) and cancer-specific mortality (death due to the cancer under investigation) among people with the highest exposure to inorganic arsenic in drinking water

Strong evidence of higher risk of lung cancer among people drinking water with high levels of arsenic or exposed to airborne arsenic

Strong evidence of higher risk of skin cancer, primarily squamous cell carcinoma, among people drinking water with high levels of arsenic

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of higher risk of breast cancer among women with higher body levels of heavy metals

Modest evidence of alterations in the microbiomethe collection of microbes living on and within your body leading to dysbiosismicrobial imbalance or maladaptation on or inside the body among people eating food contaminated with heavy metals

Bladder cancer: strong evidence of higher risk of bladder cancer among people drinking water with higher levels of arsenic

Higher risk of bladder cancer among people drinking water with high levels of arsenic in a comprehensive review of evidence¹⁰²International Agency for Research on Cancer Monograph Working Group. Arsenic, metals, fibres, and dusts. A review of human carcinogens, volume 100 C. World Health Organization. 2012.
Higher risk of bladder cancer among people drinking water containing arsenic, with increasing risk with higher levels of arsenic in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 7 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁰³Saint-Jacques N, Parker L, Brown P, Dummer TJ. Arsenic in drinking water and urinary tract cancers: a systematic review of 30 years of epidemiological evidence. Environmental Health. 2014 Jun 2;13:44.

Breast cancer: preliminary evidence of higher risk of breast cancer among women with higher body levels of heavy metals

Higher risk of breast cancer among women with higher body levels of heavy metals compared to lower levels in a systematic review of 37 observational studies¹⁰⁴Rocha PRS, Oliviera VD, Vasques CI, Dos Reis PED, Amato AM. Exposure to endocrine disruptors and risk of breast cancer: a systematic review. Critical Reviews in Oncology/Hematology. 2021 May;161:103330.

Gastrointestinal cancer: modest evidence of higher liver cancer mortality among people with the highest exposure to inorganic arsenic in drinking water

80% higher liver cancer mortality among people with the highest exposure to inorganic arsenic in drinking water compared to the lowest in a meta-analysis of 12 observational studies¹⁰⁵Wang W, Cheng S, Zhang D. Association of inorganic arsenic exposure with liver cancer mortality: a meta-analysis. Environmental Research. 2014 Nov;135:120-5.

Lung cancer: strong evidence of higher risk of lung cancer among people drinking water with high levels of arsenic or exposed to airborne arsenic

Higher risk of lung cancer among people drinking water with high levels of arsenic in a comprehensive review of evidence¹⁰⁶International Agency for Research on Cancer Monograph Working Group. Arsenic, metals, fibres, and dusts. A review of human carcinogens, volume 100 C. World Health Organization. 2012.
Higher risk of lung cancer among people exposed to airborne arsenic such as near or in metal smelters, refineries, and mines of various ores in a comprehensive review of evidence¹⁰⁷International Agency for Research on Cancer Monograph Working Group. Arsenic, metals, fibres, and dusts. A review of human carcinogens, volume 100 C. World Health Organization. 2012.

Melanoma and other skin cancer: strong evidence of higher risk of skin cancer, primarily squamous cell carcinoma, among people drinking water with high levels of arsenic

Higher risk of skin cancer among people drinking water with high levels of arsenic in a comprehensive review of evidence¹⁰⁸International Agency for Research on Cancer Monograph Working Group. Arsenic, metals, fibres, and dusts. A review of human carcinogens, volume 100 C. World Health Organization. 2012.

Your microbiome: modest evidence of alterations in the microbiome leading to dysbiosis among people eating food contaminated with heavy metals

Alterations in the microbiome leading to dysbiosis among people consuming food contaminated with heavy metals in a review of observational studies¹⁰⁹ Popli S, Badgujar PC, Agarwal T, Bhushan B, Mishra V. Persistent organic pollutants in foods, their interplay with gut microbiota and resultant toxicity. Science of the Total Environment. 2022 Aug 1;832:155084.

Asbestos

Asbestos is a mineral found in rock formations in many parts of the world. Because it is naturally resistant to heat, electricity, and corrosion, it was widely used in building and consumer products until its toxicity limited these uses. Asbestos is classified a Group 1 carcinogen—there is enough evidence to conclude that it can cause cancer in humans—by the International Agency for Research on Cancer (IARC). We draw from the IARC summary, which we consider strong evidence, and add more recent research to it.

Strong evidence of higher risk of colorectal cancer, stomach cancer, cancer of the larynx or pharynx, mesothelioma, or ovarian cancer among people exposed to asbestos

Colorectal cancer: strong evidence of higher risk of colorectal cancer among people exposed to asbestos

Higher risk of colorectal cancer among people exposed to asbestos in a comprehensive review of evidence¹¹⁰IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Arsenic, Metals, Fibres and Dusts. Lyon (FR) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 100C. Asbestos (chrysotile, amosite, crocidolite, tremolite, actinolite and anthophyllite). International Agency for Research on Cancer; 2012.

Gastrointestinal cancer: strong evidence of higher risk of stomach cancer among people exposed to asbestos

Higher risk of stomach cancer among people exposed to asbestos in a comprehensive review of evidence¹¹¹IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Arsenic, Metals, Fibres and Dusts. Lyon (FR) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 100C. Asbestos (chrysotile, amosite, crocidolite, tremolite, actinolite and anthophyllite). International Agency for Research on Cancer; 2012.

Head, neck, and oral cancer: strong evidence of higher risk of cancer of the larynx or pharynx among people exposed to asbestos

Higher risk of cancer of the larynx or pharynx among people exposed to asbestos¹¹²IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Arsenic, Metals, Fibres and Dusts. Lyon (FR) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 100C. Asbestos (chrysotile, amosite, crocidolite, tremolite, actinolite and anthophyllite). International Agency for Research on Cancer; 2012.
Higher risk of oral or pharyngeal cancer among people with occupational exposures to asbestos compared to no occupational exposures in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹¹³Paget-Bailly S, Cyr D, Luce D. Occupational exposures to asbestos, polycyclic aromatic hydrocarbons and solvents, and cancers of the oral cavity and pharynx: a quantitative literature review. International Archives of Occupational and Environmental Health. 2012 May;85(4):341-51.

Mesothelioma: strong evidence of higher risk of mesothelioma among people exposed to asbestos

Higher risk of mesothelioma among people exposed to asbestos in a comprehensive review of evidence¹¹⁴IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Arsenic, Metals, Fibres and Dusts. Lyon (FR) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 100C. Asbestos (chrysotile, amosite, crocidolite, tremolite, actinolite and anthophyllite). International Agency for Research on Cancer; 2012.

Ovarian cancer: strong evidence of higher risk of ovarian cancer among people exposed to asbestos

Higher risk of ovarian cancer among people exposed to asbestos in a comprehensive review of evidence¹¹⁵IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Arsenic, Metals, Fibres and Dusts. Lyon (FR) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 100C. Asbestos (chrysotile, amosite, crocidolite, tremolite, actinolite and anthophyllite). International Agency for Research on Cancer; 2012.

Benzene

The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions. Forest fires also produce benzene. Exposure is higher among people who manufacture or use plastics, lubricants, rubbers, dyes, detergents, drugs, and pesticides.

Good evidence of higher risk of leukemia among people exposed to benzene

Modest evidence of higher risk of non-Hodgkin lymphoma or B-cell lymphoma among people with high exposure to benzene

Bisphenol A (BPA)

Bisphenol A, or BPA, is a synthetic chemical used in plastics and resins and added to many everyday items, including cash register receipts. Most exposure comes from eating food or drinking water stored in containers that have BPA.

Body terrain

Good evidence of higher risk of type 2 diabetes among people without cancer with the highest body levels of BPA

Modest evidence of greater risk of obesity and larger waist circumference among people with the highest body levels of bisphenol A (BPA)

Preliminary evidence of higher levels of inflammation and oxidative stress among postmenopausal women with higher body levels of BPA

Symptoms

Modest evidence of higher risk of high blood pressure among people with the highest body levels of BPA

Blood sugar and insulin resistance: good evidence of higher risk of type 2 diabetes among people without cancer with the highest body levels of BPA

28% higher risk of type 2 diabetes among people with higher body levels of BPA compared to lower levels in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 16 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies of varying quality¹¹⁸Hwang S, Lim JE, Choi Y, Jee SH. Bisphenol A exposure and type 2 diabetes mellitus risk: a meta-analysis. BMC Endocrine Disorders. 2018 Nov 6;18(1):81.
Higher risk of diabetes among people with the highest body levels of BPA compared to the lowest in a meta-analysis of 12 observational studies mostly of medium quality¹¹⁹Rancière F, Lyons JG et al. Bisphenol A and the risk of cardiometabolic disorders: a systematic review with meta-analysis of the epidemiological evidence. Environmental Health. 2015 May 31;14:46.

Body weight: modest evidence of greater risk of obesity and larger waist circumference among people with the highest body levels of bisphenol A (BPA)

Higher risk of overweight, obesity and elevated waist circumference among people with the highest body levels of BPA compared to the lowest in a meta-analysis of 12 observational studies mostly of medium quality¹²⁰Rancière F, Lyons JG et al. Bisphenol A and the risk of cardiometabolic disorders: a systematic review with meta-analysis of the epidemiological evidence. Environmental Health. 2015 May 31;14:46.

Inflammation: preliminary evidence of higher levels of inflammation among postmenopausal women with higher body levels of BPA

Higher levels of biomarkers for inflammation among postmenopausal women with higher body levels of BPA compared to lower levels, but not in men or premenopausal women, in a mid-sized observational study¹²¹Yang YJ, Hong YC et al. Bisphenol A exposure is associated with oxidative stress and inflammation in postmenopausal women. Environmental Research. 2009 Aug;109(6):797-801.

Oxidative stress: preliminary evidence of higher levels of oxidative stress among postmenopausal women with higher body levels of BPA

Higher levels of biomarkers for oxidative stress and inflammation among postmenopausal women with higher body levels of BPA compared to lower levels, but not in men or premenopausal women, in a mid-sized observational study¹²²Yang YJ, Hong YC et al. Bisphenol A exposure is associated with oxidative stress and inflammation in postmenopausal women. Environmental Research. 2009 Aug;109(6):797-801.

Symptoms not related to cancer

Cardiovascular symptoms: modest evidence of higher risk of high blood pressure among people with the highest body levels of BPA

Higher risk of high blood pressure (hypertension) among people with the highest body levels of BPA compared to the lowest in a meta-analysis of 12 observational studies mostly of medium quality¹²³Rancière F, Lyons JG et al. Bisphenol A and the risk of cardiometabolic disorders: a systematic review with meta-analysis of the epidemiological evidence. Environmental Health. 2015 May 31;14:46.

Dioxins

Dioxins occur in nature but are also created by human processes. They accumulate in animal fats, including in animal-derived foods high in fat. TCDD is the primary dioxin of interest and is the most toxic. TCDD is classified a Group 1 carcinogen—there is enough evidence to conclude that it can cause cancer in humans—by the International Agency for Research on Cancer. We draw from the IARC summary, which we consider strong evidence, and add more recent research to it.

Strong evidence of higher risk of cancer as a whole, non-Hodgkin lymphoma, or soft-tissue sarcoma among people exposed to TCDD

Modest evidence of higher risk of prostate cancer among people exposed to TCDD

Cancer as a whole: strong evidence of higher risk of cancer as a whole among people exposed to TCDD

Moderately higher risk of cancer among people with the highest exposures to TCDD and the longest latency¹²⁴IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Chemical Agents and Related Occupations, Volume 100 F: A Review of Human Carcinogens. World Health Organization. 2012.
45% higher cancer mortality (3 studies) and 57% higher risk of cancer (8 studies) among people with the highest blood levels of TCDD compared to the lowest in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹²⁵Xu J, Ye Y et al. Association between dioxin and cancer incidence and mortality: a meta-analysis. Scientific Reports. 2016 Nov 29;6:38012.

Lymphoma: strong evidence of higher risk of non-Hodgkin lymphoma among people exposed to TCDD

Higher risk of non-Hodgkin lymphoma among people with exposures to TCDD in a comprehensive review of evidence¹²⁶IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Chemical Agents and Related Occupations, Volume 100 F: A Review of Human Carcinogens. World Health Organization. 2012.

Sarcoma: strong evidence of higher risk of soft-tissue sarcoma among people exposed to TCDD

Higher risk of soft-tissue sarcoma among people exposed to TCDD in a comprehensive review of evidence¹²⁷IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Chemical Agents and Related Occupations, Volume 100 F: A Review of Human Carcinogens. World Health Organization. 2012.

Prostate cancer: modest evidence of higher risk of prostate cancer among people exposed to TCDD

26% higher risk of prostate cancer among people exposed to TCDD compared to no exposure in a meta-analysis of 17 observational studies¹²⁸Leng L, Chen X, Li CP, Luo XY, Tang NJ. 2,3,7,8-Tetrachlorodibezo-p-dioxin exposure and prostate cancer: a meta-analysis of cohort studies. Public Health. 2014 Mar;128(3):207-13.

Endocrine-disrupting chemicals

Endocrine disrupting chemicals (EDCs) are any chemicals that can alter the hormonal signals that control and guide much of our growth and development, the way our organs function, and our ability to fight disease. Many pesticides are EDCs, as are some metals and many chemicals used in making common consumer products, such as phthalates and polychlorinated biphenyls (PCBs). Here we present evidence related to EDCs as a whole, PCBs, and phthalates. Evidence regarding some pesticides is assessed separately below. Bisphenol A, another EDC, is described above.

Modest evidence of hormone imbalance among women exposed to higher levels of specific endocrine-disrupting chemicals

Modest evidence of disrupted thyroid function among people with increasing body levels of diethylhexyl phthalate (DEHP)

Good evidence of substantially higher risk of osteosarcoma or lymphoma among children exposed to phthalates in medications

Preliminary evidence of higher risk of breast cancer among women with higher body levels of phthalates or PCBs

Your body terrain

Modest evidence of hormone imbalance among women exposed to higher levels of specific endocrine-disrupting chemicals

Modest evidence of disrupted thyroid function among people with increasing body levels of diethylhexyl phthalate (DEHP)

Earlier onset of menopause by 1.9 to 3.8 years among women over age 30 with higher body levels of endocrine disrupting chemicals [β-hexachlorocyclohexane, mirex, p,p’-DDE, 1,2,3,4,6,7,8-heptachlorodibenzofuran, mono-(2-ethyl-5-hydroxyhexyl) and mono-(2-ethyl-5-oxohexyl) phthalate, polychlorinated biphenyl congeners -70, -99, -105, -118, -138, -153, -156, -170, and -183] compared to lower levels in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹²⁹Grindler NM, Allsworth JE et al. Persistent organic pollutants and early menopause in U.S. women. PLoS One. 2015 Jan 28;10(1):e0116057.
10% decrease in follicle stimulating hormone in premenopausal women aged 18-44 with higher body levels of cadmium compared to lower levels in a mid-sized observational study¹³⁰Pollack AZ, Schisterman EF et al. Cadmium, lead, and mercury in relation to reproductive hormones and anovulation in premenopausal women. Environmental Health Perspectives. 2011 Aug;119(8):1156-61.
Increasing markers of disrupted thyroid function among people with increasing body levels of diethylhexyl phthalate (DEHP) in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 13 observational studies¹³¹Kim MJ, Moon S et al. Association between diethylhexyl phthalate exposure and thyroid function: a meta-analysis. Thyroid. 2019 Feb;29(2):183-192.

Cancer risk

Good evidence of substantially higher risk of osteosarcoma and lymphoma among children exposed to phthalates in medications

Preliminary evidence of higher risk of breast cancer among women with higher body levels of phthalates or PCBs

278% higher risk (nearly triple) of osteosarcoma among children exposed to phthalates in medications used from before birth until age 19 compared to other children in a very large observational study¹³²Ahern TP, Spector LG et al. Medication-associated phthalate exposure and childhood cancer incidence. Journal of the National Cancer Institute. 2022 Feb 18:djac045.
207% higher risk (more than double) of Hodgkin and non-Hodgkin lymphoma but not Burkitt lymphoma among children exposed to phthalates in medications used from before birth until age 19 compared to other children in a very large observational study¹³³Ahern TP, Spector LG et al. Medication-associated phthalate exposure and childhood cancer incidence. Journal of the National Cancer Institute. 2022 Feb 18:djac045.
Higher risk of breast cancer among women with higher body levels of phthalates or PCBs compared to lower levels in a systematic review of 37 observational studies¹³⁴Rocha PRS, Oliviera VD, Vasques CI, Dos Reis PED, Amato AM. Exposure to endocrine disruptors and risk of breast cancer: a systematic review. Critical Reviews in Oncology/Hematology. 2021 May;161:103330.

Formaldehyde

Formaldehyde-based resins are used in the manufacture of plywood, particleboard, furniture, cabinets, and other composite wood products. Formaldehyde is used in many cosmetic products as a preservative. Formaldehyde is also produced when smoking tobacco or using unvented fuel-burning appliances such as gas stoves or kerosene space heaters.

Formaldehyde is classified a Group 1 carcinogen—there is enough evidence to conclude that it can cause cancer in humans—by the International Agency for Research on Cancer (IARC). We draw from the IARC summary, which we consider strong evidence, and add more recent research to it.

Modest evidence of higher risk of brain cancer among people with the highest exposures to formaldehyde

Strong evidence of higher risk of nasopharyngeal cancer among people exposed to formaldehyde

Modest evidence of higher risk of sinonasal cancer among people with occupational exposure to formaldehyde

Good evidence of higher risk of leukemia among people with occupational exposure to formaldehyde

Weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of lung cancer among people with the highest occupational exposures to formaldehyde

No evidence of an effect on risk of non-Hodgkin lymphoma among people with occupational exposure to formaldehyde in a combined analysis of studies

Brain cancer: modest evidence of higher risk of brain cancer among people with the highest exposures to formaldehyde

71% higher risk of brain cancer among people with the highest exposures to formaldehyde compared to no or low exposure in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 12 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹³⁵Rana I, Rieswijk L, Steinmaus C, Zhang L. Formaldehyde and brain disorders: a meta-analysis and bioinformatics approach. Neurotoxicity Research. 2021 Jun;39(3):924-948.

Head, neck, and oral cancer

Strong evidence of higher risk of nasopharyngeal cancer among people exposed to formaldehyde

Modest evidence of higher risk of sinonasal cancer among people with occupational exposure to formaldehyde

Higher risk of nasopharyngeal cancer among people exposed to formaldehyde in a comprehensive review of evidence¹³⁶IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 88: Formaldehyde, 2-Butoxyethanol and 1-tert-Butoxypropan-2-ol. World Health Organization. 2006.
Higher risk of sinonasal cancer among people with occupational exposure to formaldehyde compared to no occupational exposure in a meta-analysis of a subset of 28 observational studies¹³⁷Binazzi A, Ferrante P, Marinaccio A. Occupational exposure and sinonasal cancer: a systematic review and meta-analysis. BMC Cancer. 2015 Feb 13;15:49.

Leukemia: good evidence of higher risk of leukemia among people with occupational exposure to formaldehyde

Higher risk of leukemia among people with occupational exposure to formaldehyde in a comprehensive review of evidence¹³⁸IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 88: Formaldehyde, 2-Butoxyethanol and 1-tert-Butoxypropan-2-ol. World Health Organization. 2006.

Lung cancer: weak evidence of lung cancer among people with the highest occupational exposures to formaldehyde

A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward increased risk of lung cancer among people with the highest occupational exposures to formaldehyde compared to no occupational exposure in a meta-analysis of 31 observational studies¹³⁹Kwak K, Paek D, Park JT. Occupational exposure to formaldehyde and risk of lung cancer: A systematic review and meta-analysis. American Journal of Industrial Medicine. 2020 Apr;63(4):312-327.

Lymphoma: no evidence of an effect on risk of non-Hodgkin lymphoma among people with occupational exposure to formaldehyde in a combined analysis of studies

No evidence of an effect on risk of non-Hodgkin lymphoma among people with occupational exposure to formaldehyde compared to no occupational exposure in a meta-analysis of 12 observational studies¹⁴⁰Catalani S, Donato F et al. Occupational exposure to formaldehyde and risk of non hodgkin lymphoma: a meta-analysis. BMC Cancer. 2019 Dec 23;19(1):1245.

Hair dye or straightener

Hair dyes and straighteners are cosmetic products applied to the hair to alter color or straighten curly or kinky hair.

Weak evidence of slightly lower risk of cancer and cancer-related death as a whole, brain cancer, leukemia, or small lymphocytic lymphoma among people ever using hair dye

Modest evidence of slightly increased risk of breast cancer among people using permanent hair dye Preliminary evidence of slightly increased risk of breast cancer among people applying semi-permanent dye to others non-professionally

Weak evidence of higher risk of breast cancer among women with a sister with breast cancer and using hair straightener or applying it to others non-professionally

Weak evidence of a slightly higher risk of colorectal cancer, ovarian cancer, or basal cell carcinoma among people ever using hair dye

Modest evidence of higher incidence of uterine cancer among women using hair straighteners

Modest evidence of higher risk of Hodgkin lymphoma among people ever using hair dye

Cancer as a whole: weak evidence of slightly lower risk of cancer as a whole and cancer-related mortality among people ever using hair dye

A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward lower risk of cancer as a whole and cancer-related mortality among people ever using hair dye compared to non-users in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁴¹Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.

Brain cancer: weak evidence of slightly lower risk of brain cancer among people ever using hair dye

A weak trend toward lower risk of brain cancer among people ever using hair dye compared to non-users in a very large observational study¹⁴²Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.

Breast cancer

Modest evidence of slightly higher risk of breast cancer among people using permanent hair dye Preliminary evidence of slightly increased risk of breast cancer among people applying semi-permanent dye to others non-professionally

Weak evidence of higher risk of breast cancer among women with a sister with breast cancer and using hair straightener or applying it to others non-professionally

18.8% higher risk of breast cancer among people using hair dye compared to no use in a large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 8 observational studies¹⁴³Gera R, Mokbel R, Igor I, Mokbel K. Does the use of hair dyes increase the risk of developing breast cancer? A meta-analysis and review of the literature. Anticancer Research. 2018 Feb;38(2):707-716.
45% higher risk of breast cancer among black American women without cancer at baseline and with a sister with cancer, and a weak trend toward slightly higher risk among white women, using permanent hair dye compared to non-users in a large observational study¹⁴⁴Eberle CE, Sandler DP, Taylor KW, White AJ. Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women. International Journal of Cancer. 2019 Dec 3.
28% increased risk of breast cancer among women without cancer at baseline and with a sister with breast cancer applying semi-permanent hair dye to others (non-professional applications) compared to other women in a large observational study¹⁴⁵Eberle CE, Sandler DP, Taylor KW, White AJ. Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women. International Journal of Cancer. 2019 Dec 3.
A weak trend toward higher risk of breast cancer, with the strongest effect with PR-negative cancer, among people ever using hair dye compared to non-users in a very large observational study¹⁴⁶Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.
A weak trend toward higher risk of breast cancer among women without cancer at baseline and with a sister with cancer, and using hair straightener, or applying hair straightener to others (non-professional applications) compared to non-users, with higher risks among those using straighteners more often, in a large observational study¹⁴⁷Eberle CE, Sandler DP, Taylor KW, White AJ. Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women. International Journal of Cancer. 2019 Dec 3.

Colorectal cancer: weak evidence of a slightly higher risk of colorectal cancer among people ever using hair dye

A weak trend toward higher risk of colorectal cancer among people ever using hair dye compared to non-users in a very large observational study¹⁴⁸Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.

Gynecological cancers: modest evidence of higher incidence of uterine cancer among women using hair straighteners

80% higher incidence of uterine cancer among women using hair straighteners, with even higher incidence among frequent users compared to never-users in a very large observational study¹⁴⁹Chang CJ, O’Brien KM et al. Use of straighteners and other hair products and incident uterine cancer. Journal of the National Cancer Institute. 2022 Oct 17:djac165.

Leukemia or lymphoma

Modest evidence of higher risk of Hodgkin lymphoma among people ever using hair dye

Weak evidence of slightly lower risk of leukemia or small lymphocytic lymphoma among people ever using hair dye

Moderately higher risk of Hodgkin lymphoma among people ever using hair dye compared to non-users in a very large observational study¹⁵⁰Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.
A weak trend toward lower risk of chronic lymphocytic leukemia or small lymphocytic lymphoma among people ever using hair dye compared to non-users in a very large observational study¹⁵¹Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.

Ovarian cancer: weak evidence of a slightly higher risk of ovarian cancer among people ever using hair dye

A weak trend toward higher risk of ovarian cancer among people ever using hair dye compared to non-users in a very large observational study¹⁵²Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.

Skin cancer: weak evidence of a slightly higher risk of basal cell carcinoma among people ever using hair dye

Slightly higher risk of basal cell carcinoma among people ever using hair dye compared to non-users in a very large observational study¹⁵³Zhang Y, Birmann BM et al. Personal use of permanent hair dyes and cancer risk and mortality in US women: prospective cohort study. BMJ. 2020 Sep 2;370:m2942.

Perfluoroalkyl substances (PFAS)

Perfluorinated chemicals are manufactured chemicals used widely in non-stick cookware, stain-resistant fabrics, and fire-fighting foams.

Modest evidence of lower immune response to vaccines among children exposed to higher levels of PFAS (perfluoroalkyl substances)

Preliminary evidence of increased risk of kidney or testicular cancers among people with greater exposure to PFOA, a perfluorinated chemical

Your body terrain

Immune function: modest evidence of changes in immune function among children exposed to higher levels of PFAS

Lower immune response to vaccines for tetanus and/or diphtheria among children aged 5 to 7 years exposed to higher levels of PFAS compared to lower levels in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁵⁴Grandjean P, Andersen EW et al. Serum vaccine antibody concentrations in children exposed to perfluorinated compounds. JAMA. 2012 Jan 25;307(4):391-7.
Higher incidence of bronchitis/pneumonia, throat infection, pseudocroup, ear infection, and gastric flu/diarrhea, but lower incidence of eczema, pseudocroup, ear infections, and urinary tract infections among girls aged 3 and 7 with higher PFAS exposures before birth in a large observational study¹⁵⁵Impinen A, Longnecker MP et al. Maternal levels of perfluoroalkyl substances (PFASs) during pregnancy and childhood allergy and asthma related outcomes and infections in the Norwegian Mother and Child (MoBa) cohort. Environment International. 2019 Mar;124:462-472.
A weak trend toward higher asthma prevalence among US children with higher body levels of PFAS in a mid-sized observational study¹⁵⁶Jackson-Browne MS, Eliot M, Patti M, Spanier AJ, Braun JM. PFAS (per- and polyfluoroalkyl substances) and asthma in young children: NHANES 2013-2014. International Journal of Hygiene and Environmental Health. 2020 Aug;229:113565.

Cancer risk

Preliminary evidence of increased risk of kidney and testicular cancers among people with greater exposure to PFOA, a perfluorinated chemical

16% higher risk of kidney cancer and 3% higher risk of testicular cancer with each 10 ng/mL increase in serum PFOA among people in a review of 10 observational studies¹⁵⁷Bartell SM, Vieira VM. Critical review on PFOA, kidney cancer, and testicular cancer. Journal of the Air & Waste Management Association. 2021 Jun;71(6):663-679.

Pesticides

Pesticides include all products meant to kill, repel, or control living organisms: herbicides, insecticides, rodenticides, nematicides, fungicides, and more. Because pesticide residues on food is common, we consider evidence regarding eating organic food an indication of less exposure to pesticides.

Although DDT was banned in the US in 1972, residues are still present in some foods, and people continue to be exposed. Animal and fatty foods contain the highest levels of DDT. This pesticide is still actively used in some countries, especially those with a high incidence of malaria.

Preliminary evidence of increased mortality among women with breast cancer with higher blood levels of an organochlorine pesticide

Modest evidence of lower risk of overweight and obesity among people without cancer consuming organic foods more frequently and therefore less exposed to pesticide residues

Strong evidence of immunosuppressionpartial or complete suppression of the immune response among people with higher exposures to DDT

Modest evidence of alterations in the microbiome leading to dysbiosis among people eating food contaminated with pesticides or directly exposed to pesticides

Insufficient (conflicting) evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of cancer among adults eating organic foods

Modest evidence of substantially higher risk of breast cancer among people exposed to some pesticides

Modest evidence of higher risk of brain tumors among children and young adults exposed to higher levels of residential pesticides

Good evidence of higher risk of childhood leukemia or lymphoma among children exposed to higher levels of indoor pesticides

Cancer survival

Preliminary evidence of increased mortality among women with breast cancer with higher blood levels of an organochlorine pesticide

Substantially higher (more than double) cancer-specific and overall mortality among women with breast cancer with higher levels of dieldrin, an organochlorine pesticide, in their blood compared to women with breast cancer with lower levels of dieldrin in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁵⁸Høyer AP, Jørgensen T, Brock JW, Grandjean P. Organochlorine exposure and breast cancer survival. Journal of Clinical Epidemiology. 2000 Mar 1;53(3):323-30.

Your body terrain

Strong evidence of immunosuppression among people with higher exposures to DDT

Modest evidence of lower risk of obesity and elevated waist circumference among people eating organic foods

Modest evidence of alterations in the microbiome leading to dysbiosis among people eating food contaminated with pesticides or directly exposed to pesticides

Immune function: strong evidence of immunosuppression among people with higher exposures to DDT

Higher risk of immunosuppression among people with higher exposures to DDT in a comprehensive review of evidence¹⁵⁹IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 113: DDT, Lindane, and 2,4-D. World Health Organization. 2018.

Body weight: modest evidence of lower risk of obesity and elevated waist circumference among people eating organic foods

16% lower increase in body mass index (BMI) and 8% lower risk of overweight and obesity among people, primarily middle-aged women, eating organic foods most frequently compared to least frequently in a large observational study¹⁶⁰Kesse-Guyot E, Baudry J, et al. Prospective association between consumption frequency of organic food and body weight change, risk of overweight or obesity: results from the NutriNet-Santé Study. British Journal of Nutrition. 2017 Jan;117(2):325-334.

Your microbiome: modest evidence of alterations in the microbiome leading to dysbiosis among people eating food contaminated with pesticides or directly exposed to pesticides

Alterations in the microbiome leading to dysbiosis among people consuming food contaminated with pesticides or directly exposed to pesticides in reviews of observational studies¹⁶¹Lima C, Falcão MAP, Rosa JGS, Disner GR, Lopes-Ferreira M. Pesticides and their impairing effects on epithelial barrier integrity, dysbiosis, disruption of the AhR signaling pathway and development of immune-mediated inflammatory diseases. International Journal of Molecular Sciences. 2022 Oct 17;23(20):12402; Gama J, Neves B, Pereira A. Chronic effects of dietary pesticides on the gut microbiome and neurodevelopment. Frontiers in Microbiology. 2022 Jun 30;13:931440; Popli S, Badgujar PC, Agarwal T, Bhushan B, Mishra V. Persistent organic pollutants in foods, their interplay with gut microbiota and resultant toxicity. Science of the Total Environment. 2022 Aug 1;832:155084.

Cancer risk

Modest evidence of higher risk of several types of cancer among greenspace workers with occupational pesticide exposure

Insufficient (conflicting) evidence of lower risk of cancer among adults eating organic foods

Modest evidence of higher risk of brain tumors among children and young adults exposed to higher levels of residential pesticides

Modest evidence of higher risk of nervous system tumors among agricultural and greenspace workers characterized by higher exposures to pesticides

Modest evidence of substantially higher risk of breast cancer among people exposed to some pesticides

Preliminary evidence of higher risk of breast cancer among women with higher body levels of organochlorine pesticides

Good evidence of higher risk of liver cancer, non-Hodgkin lymphoma, or testicular cancer among people exposed to DDT

Good evidence of higher risk of childhood leukemia or lymphoma among children exposed to higher levels of indoor pesticides

Modest evidence of lower risk of non-Hodgkin lymphoma among women eating organic foods

Cancer as a whole

Modest evidence of higher risk of several types of cancer among greenspace workers with occupational pesticide exposure

Insufficient (conflicting) evidence of lower risk of cancer among adults eating organic foods

Higher risk of several types of cancer, including leukemia, soft-tissue sarcoma, multiple myeloma, and non-Hodgkin lymphoma, among greenspace workers with occupational pesticide exposure compared to other people in a review of observational studies¹⁶²de Graaf L, Boulanger M et al. Occupational pesticide exposure, cancer and chronic neurological disorders: a systematic review of epidemiological studies in greenspace workers. Environmental Research. 2022 Jan;203:111822.

Insufficient (conflicting) evidence of lower risk of cancer as a whole among adults eating organic foods

25% lower risk of cancer among adults, around 80% of whom were female, eating organic foods most frequently compared to least frequently in a very large observational study¹⁶³Baudry J, Assmann KE et al. Association of frequency of organic food consumption with cancer risk: findings from the NutriNet-Santé Prospective Cohort Study. JAMA Internal Medicine. 2018 Dec 1;178(12):1597-1606.
No change in overall risk of cancer or of most common cancers among women eating organic foods most frequently compared to least frequently in a very large observational study¹⁶⁴Bradbury KE, Balkwill A et al. Organic food consumption and the incidence of cancer in a large prospective study of women in the United Kingdom. British Journal of Cancer. 2014 Apr 29;110(9):2321-6.

Brain or nervous system cancer

Modest evidence of higher risk of brain tumors among children and young adults exposed to higher levels of residential pesticides

Modest evidence of higher risk of nervous system tumors among agricultural and greenspace workers characterized by higher exposures to pesticides

26% higher risk of brain tumors among children and young adults exposed to higher levels of residential pesticides compared to lower levels in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 18 observational studies¹⁶⁵Van Maele-Fabry G, Gamet-Payrastre L, Lison D. Residential exposure to pesticides as risk factor for childhood and young adult brain tumors: a systematic review and meta-analysis. Environment International. 2017 Sep;106:69-90.
A weak trend toward higher risk of brain tumors among children exposed to higher levels of residential pesticides including herbicides compared to lower levels in a meta-analysis of 16 observational studies¹⁶⁶Chen M, Chang CH, Tao L, Lu C. Residential exposure to pesticide during childhood and childhood cancers: a meta-analysis. Pediatrics. 2015 Oct;136(4):719-29.
Higher risk of nervous system tumors among agricultural and greenspace workers characterized by higher exposures to pesticides in a large observational study¹⁶⁷Baldi I, De Graaf L et al. Occupational exposure to pesticides and central nervous system tumors: results from the CERENAT case-control study. Cancer Causes & Control. 2021 Jul;32(7):773-782.

Breast cancer

Modest evidence of substantially higher risk of breast cancer among people exposed to some pesticides

Preliminary evidence of higher risk of breast cancer among women with higher body levels of organochlorine pesticides

Substantially higher risk (3 times as high) of postmenopausal breast cancer among women previously exposed to the organophosphate insecticide chlorpyrifos at residences, workplaces, or both places compared to other people, but no increased risk with exposures to select organochlorine pesticides in a mid-sized observational study¹⁶⁸Tayour C, Ritz B, Langholz B, Mills PK, Wu A, Wilson JP, Shahabi K, Cockburn M. A case-control study of breast cancer risk and ambient exposure to pesticides. Environmental Epidemiology. 2019 Oct 14;3(5):e070.
Substantially higher risk (5 times as high) of breast cancer before age 50 among women with high blood levels of DDT as young adults and exposed before age 14 compared to women not exposed before age 14 in a mid-sized observational study¹⁶⁹Cohn BA, Wolff MS, Cirillo PM, Sholtz RI. DDT and breast cancer in young women: new data on the significance of age at exposure. Environmental Health Perspectives. 2007 Oct;115(10):1406-14.
Higher risk of breast cancer among women with higher body levels of organochlorine pesticides compared to lower levels in a systematic review of 37 observational studies¹⁷⁰Rocha PRS, Oliviera VD, Vasques CI, Dos Reis PED, Amato AM. Exposure to endocrine disruptors and risk of breast cancer: a systematic review. Critical Reviews in Oncology/Hematology. 2021 May;161:103330.

Gastrointestinal cancer: good evidence of higher risk of liver cancer among people exposed to DDT

Higher risk of liver cancer among people exposed to DDT in a comprehensive review of evidence¹⁷¹IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 113: DDT, Lindane, and 2,4-D. World Health Organization. 2018.

Leukemia or lymphoma

Good evidence of higher risk of childhood leukemia or lymphoma among children exposed to higher levels of indoor pesticides

Good evidence of higher risk of non-Hodgkin lymphoma among people exposed to DDT

Modest evidence of lower risk of non-Hodgkin lymphoma among women eating organic foods

Higher risk of childhood leukemia or lymphoma among children exposed to higher levels of indoor insecticides—but not outdoor residential insecticides—compared to lower levels in a meta-analysis of 16 observational studies¹⁷²Chen M, Chang CH, Tao L, Lu C. Residential exposure to pesticide during childhood and childhood cancers: a meta-analysis. Pediatrics. 2015 Oct;136(4):719-29.
Higher risk of leukemia among children exposed to higher levels of herbicides compared to lower levels in a meta-analysis of 16 observational studies¹⁷³Chen M, Chang CH, Tao L, Lu C. Residential exposure to pesticide during childhood and childhood cancers: a meta-analysis. Pediatrics. 2015 Oct;136(4):719-29.
Higher risk of non-Hodgkin lymphoma among people exposed to DDT in a comprehensive review of evidence¹⁷⁴IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 113: DDT, Lindane, and 2,4-D. World Health Organization. 2018.
21% lower risk of non-Hodgkin lymphoma among women eating organic foods most frequently compared to those consuming organic foods least frequently in a very large observational study¹⁷⁵Bradbury KE, Balkwill A et al. Organic food consumption and the incidence of cancer in a large prospective study of women in the United Kingdom. British Journal of Cancer. 2014 Apr 29;110(9):2321-6.

Testicular cancer: good evidence of higher risk of testicular cancer among people exposed to DDT

Higher risk of testicular cancer among people exposed to DDT in a comprehensive review of evidence¹⁷⁶IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 113: DDT, Lindane, and 2,4-D. World Health Organization. 2018.

Polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are toxic substances formed during combustion, including burning tobacco when smoking or grilling meat. Most of the studies showing an association with cancer involve occupational exposures which are typically far higher than you would have at home.

Good evidence of higher risk of lung cancer among workers in some industries with high occupational exposures to PAHs

Modest evidence of slightly higher risk of cancer as a whole among people living in urban areas characterized by higher concentrations of PAHs

Preliminary evidence of higher risk of childhood cancer among children exposed to PAHs from playgrounds surfaced with poured rubber

Modest evidence of higher risk of bladder cancer, breast cancer, or oral cancer among people with occupational exposures to PAHs

Weak evidence of higher risk of Hodgkin lymphoma among foundry workers with occupational exposures to PAHs

Cancer as a whole:

Modest evidence of slightly higher risk of cancer as a whole among people living in urban areas characterized by higher concentrations of PAHs

Preliminary evidence of higher risk of childhood cancer among children exposed to PAHs from playgrounds surfaced with poured rubber

Slightly higher risk of cancer as a whole among people living in urban areas characterized by higher concentrations of PAHs compared to lower concentrations in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁷⁷Huang F, Zhang Y et al. Characterization, sources and excessive cancer risk of pm2.5-bound polycyclic aromatic hydrocarbons in different green spaces in Lin’an, Hangzhou, China. Bulletin of Environmental Contamination and Toxicology. 2021 Sep;107(3):519-529.
Higher risk of childhood cancer among children exposed to PAHs from playgrounds surfaced with poured rubber compared to uncovered soil playgrounds in an observational study¹⁷⁸Tarafdar A, Oh MJ, Nguyen-Phuong Q, Kwon JH. Profiling and potential cancer risk assessment on children exposed to PAHs in playground dust/soil: a comparative study on poured rubber surfaced and classical soil playgrounds in Seoul. Environmental Geochemistry and Health. 2020 Jun;42(6):1691-1704.

Bladder cancer: modest evidence of higher risk of bladder cancer among people with occupational exposures to PAHs

Marginally higher risk of bladder cancer among people with occupational exposures to PAHs compared to no occupational exposures in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 13 observational studies¹⁷⁹Rota M, Bosetti C, Boccia S, Boffetta P, La Vecchia C. Occupational exposures to polycyclic aromatic hydrocarbons and respiratory and urinary tract cancers: an updated systematic review and a meta-analysis to 2014. Archives of Toxicology. 2014 Aug;88(8):1479-90.
Higher bladder cancer mortality among people with occupational exposures to PAHs compared to no occupational exposures in a meta-analysis of a subset of 263 observational studies¹⁸⁰Cumberbatch MG, Cox A, Teare D, Catto JW. Contemporary occupational carcinogen exposure and bladder cancer: a systematic review and meta-analysis. JAMA Oncology. 2015 Dec;1(9):1282-90.

Breast cancer: modest evidence of higher risk of breast cancer among people with occupational exposures to PAHs

Higher risk of breast cancer among people with occupational exposures to PAHs compared to no occupational exposures in a meta-analysis of 23 observational studies¹⁸¹Gamboa-Loira B, López-Carrillo L, Mar-Sánchez Y, Stern D, Cebrián ME. Epidemiologic evidence of exposure to polycyclic aromatic hydrocarbons and breast cancer: a systematic review and meta-analysis. Chemosphere. 2022 Mar;290:133237.

Head, neck, and oral cancer: modest evidence of higher risk of laryngeal, oral, or pharyngeal cancer among people with occupational exposures to PAHs

Higher risk of laryngeal cancer and cancer mortality among people with occupational exposures to PAHs compared to no occupational exposures in a meta-analysis of 16 observational studies¹⁸²Wagner M, Bolm-Audorff U et al. Occupational polycyclic aromatic hydrocarbon exposure and risk of larynx cancer: a systematic review and meta-analysis. Occupational and Environmental Medicine. 2015 Mar;72(3):226-33.
Slightly higher risk of oral or pharyngeal cancer among people with occupational exposures to PAHs compared to no occupational exposures in a meta-analysis of observational studies¹⁸³Paget-Bailly S, Cyr D, Luce D. Occupational exposures to asbestos, polycyclic aromatic hydrocarbons and solvents, and cancers of the oral cavity and pharynx: a quantitative literature review. International Archives of Occupational and Environmental Health. 2012 May;85(4):341-51.

Lung cancer: good evidence of higher risk of lung cancer among workers in some industries with high occupational exposures to PAHs

Moderately higher (about 50% higher) risk of lung cancer among workers in coal/coke and foundry industries with occupational exposures to PAHs compared to no occupational exposures in a very large meta-analysis of 24 observational studies¹⁸⁴Singh A, Kamal R et al. PAH exposure-associated lung cancer: an updated meta-analysis. Occupational Medicine (Lond). 2018 May 23;68(4):255-261.
Higher risk of respiratory tract cancer, mainly lung cancer, among people with occupational exposures to PAHs compared to no occupational exposures in a meta-analysis of 13 observational studies¹⁸⁵Rota M, Bosetti C, Boccia S, Boffetta P, La Vecchia C. Occupational exposures to polycyclic aromatic hydrocarbons and respiratory and urinary tract cancers: an updated systematic review and a meta-analysis to 2014. Archives of Toxicology. 2014 Aug;88(8):1479-90.

Lymphoma: weak evidence of higher risk of Hodgkin lymphoma among foundry workers with occupational exposures to PAHs

A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward higher risk of Hodgkin lymphoma among foundry workers with occupational exposures to PAHs compared to no occupational exposures in a meta-analysis of 12 observational studies¹⁸⁶Alicandro G, Rota M, Boffetta P, La Vecchia C. Occupational exposure to polycyclic aromatic hydrocarbons and lymphatic and hematopoietic neoplasms: a systematic review and meta-analysis of cohort studies. Archives of Toxicology. 2016 Nov;90(11):2643-2656.

Vinyl chloride

Vinyl chloride is used in making PVC (polyvinyl chloride) plastic, used widely in construction and in wire coatings, vehicle upholstery, and plastic kitchen wares. Vinyl chloride is classified a Group 1 carcinogen—there is enough evidence to conclude that it can cause cancer in humans—by the International Agency for Research on Cancer (IARC). We draw from the IARC summary, which we consider strong evidence, and add more recent research to it.

Strong evidence of higher risk of liver cancer among people with occupational exposure to vinyl chloride

Wood dust

Wood dust is created during woodworking. It is classified a Group 1 carcinogen—there is enough evidence to conclude that it can cause cancer in humans—by the International Agency for Research on Cancer (IARC). We draw from the IARC summary, which we consider strong evidence, and add more recent research to it.

Strong evidence of a higher risk of cancer as a whole among people exposed to wood dust

Modest evidence of higher risk of nasal adenocarcinoma, nasopharyngeal cancer, or lung cancer among people with occupational exposure to wood dust

Cancer as a whole: strong evidence of a higher risk of cancer as a whole among people exposed to wood dust

Higher risk of cancer as a whole among people exposed to wood dust in a comprehensive review of evidence¹⁸⁹IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Wood Dust and Formaldehyde. World Health Organization. 1995.

Head, neck, and oral cancer: modest evidence of higher risk of nasal adenocarcinoma and nasopharyngeal cancer among people with occupational exposure to wood dust

Higher risk of nasal adenocarcinoma among people with occupational exposure to wood dust in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 22 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁹⁰Alonso-Sardón M, Chamorro AJ et al. Association between occupational exposure to wood dust and cancer: a systematic review and meta-analysis. PLoS One. 2015 Jul 20;10(7):e0133024.
Higher risk of nasopharyngeal cancer among people with occupational exposure to wood dust in a meta-analysis of 7¹⁹¹Beigzadeh Z, Pourhassan B, Kalantary S, Golbabaei F. Occupational exposure to wood dust and risk of nasopharyngeal cancer: A systematic review and meta-analysis. Environmental Research. 2019 Apr;171:170-176. and 11¹⁹²E M, Yin J et al. Wood dust exposure and risks of nasopharyngeal carcinoma: a meta-analysis. European Journal of Public Health. 2020 Aug 1;30(4):817-822. observational studies
Higher risk of sinonasal cancer, especially adenocarcinomas, among people with occupational exposure to wood dust compared to no occupational exposure in a meta-analysis of a subset of 28 observational studies¹⁹³Binazzi A, Ferrante P, Marinaccio A. Occupational exposure and sinonasal cancer: a systematic review and meta-analysis. BMC Cancer. 2015 Feb 13;15:49.

Lung cancer: modest evidence of higher risk of lung cancer among people with occupational exposure to wood dust

21% higher risk of lung cancer among people with occupational exposure to wood dust, although lower risk in countries in which softwood exposures dominate in a meta-analysis of 33 observational studies¹⁹⁴Hancock DG, Langley ME, Chia KL, Woodman RJ, Shanahan EM. Wood dust exposure and lung cancer risk: a meta-analysis. Occupational and Environmental Medicine. 2015 Dec;72(12):889-98.

Other environmental exposures

Nighttime work

Many occupations involve working at night, either regularly or as part of rotating shifts. Nighttime work has mixed outcomes regarding cancer risk and survival, with benefits in some types of cancer and worse outcomes with others.

Cancer survival

Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of higher mortality from cardiovascular causes among people with breast cancer working night shifts or rotating night shift work

Cancer risk

Higher risk

Good evidence of slightly higher risk of cancer mortality among people without cancer at baseline working at night

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of a slightly higher risk of stomach cancer among people working at night

Preliminary (conflicting) evidence of higher risk of prostate cancer among people working at night

No evidence of an effect or unknown effect

Insufficient (conflicting) evidencepreclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example) (this is the CancerChoices definition; other researchers and studies may define this differently) of any higher risk of breast cancer among people working at night

No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of colorectal cancer, non-Hodgkin lymphoma, ovarian cancer, or pancreatic cancer among people working at night in a combined analysis of studies

Lower risk

Good evidence of lower risk of lung cancer or skin cancer among people working at night

Body terrain factors

Good evidence of higher risk of impaired glucose tolerance and diabetes among people working at night

Cancer survival

Good evidence of higher mortality from cardiovascular causes among people with breast cancer working night shifts or rotating night shift work

Slightly higher all-cause mortality, mostly from cardiovascular causes, among people with breast cancer with night shift work or rotating night shift work compared to day work in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 16 studies¹⁹⁵Lin X, Chen W et al. Night-shift work increases morbidity of breast cancer and all-cause mortality: a meta-analysis of 16 prospective cohort studies. Sleep Medicine. 2015 Nov;16(11):1381-1387.

Cancer risk

Cancer as a whole: good evidence of slightly higher risk of cancer mortality among people without cancer at baseline working at night

Slightly (4%) higher cancer mortality among people without cancer at baseline working at night compared to daytime work in a very large meta-analysis of 17 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies, 15 of which were relatively high quality¹⁹⁶Su F, Huang D, Wang H, Yang Z. Associations of shift work and night work with risk of all-cause, cardiovascular and cancer mortality: a meta-analysis of cohort studies. Sleep Medicine. 2021 Oct;86:90-98.
Slightly higher risk of cancer as a whole among people working the greatest number of night shifts, or in some studies any night shifts, compared to no night shifts in a very large meta-analysis of marginal quality of 57 observational studies¹⁹⁷Liu W, Zhou Z, Dong D, Sun L, Zhang G. Sex differences in the association between night shift work and the risk of cancers: a meta-analysis of 57 articles. Disease Markers. 2018 Nov 26;2018:7925219.

Breast cancer: insufficient (conflicting) evidence of any higher risk of breast cancer among people working at night

No evidence of an effect on risk of breast cancer among people working night shifts, whether briefly or more than 30 years, compared to no shift work in a very large meta-analysis of observational studies¹⁹⁸Travis RC, Balkwill A et al. Night shift work and breast cancer incidence: three prospective studies and meta-analysis of published studies. Journal of the National Cancer Institute. 2016 Oct 6;108(12):djw169.
No evidence of an effect on risk of breast cancer among people working at night compared to no night work in a very large meta-analysis of 57 observational studies¹⁹⁹Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.
Slightly higher risk of breast cancer among people working the greatest number of night shifts, or in some studies any night shifts, compared to no night shifts in a very large meta-analysis of marginal quality of 57 observational studies²⁰⁰Liu W, Zhou Z, Dong D, Sun L, Zhang G. Sex differences in the association between night shift work and the risk of cancers: a meta-analysis of 57 articles. Disease Markers. 2018 Nov 26;2018:7925219.
Slightly higher risk of breast cancer among people working night shifts or rotating night shift work, with higher risks with more years of night work (rising from less than 3% higher risk with fewer than 10 years of night shift work to 6–9% higher risk with more than 10 years), compared to day work in a very large meta-analysis of 16 studies²⁰¹Lin X, Chen W et al. Night-shift work increases morbidity of breast cancer and all-cause mortality: a meta-analysis of 16 prospective cohort studies. Sleep Medicine. 2015 Nov;16(11):1381-1387.
19% higher risk of breast cancer among people working night shifts and 12% higher risk with exposure to light at night compared to other people in a meta-analysis of 28 observational studies²⁰²He C, Anand ST, Ebell MH, Vena JE, Robb SW. Circadian disrupting exposures and breast cancer risk: a meta-analysis. International Archives of Occupational and Environmental Health. 2015 Jul;88: 533-47.

Colorectal cancer: no evidence of an effect on risk of colorectal cancer among people working night shifts in a combined analysis of studies

No evidence of an effect on risk of colorectal cancer among people working at night compared to no night work in a very large meta-analysis of 57 observational studies²⁰³Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.

Gastrointestinal cancer: preliminary evidence of a slightly higher risk of stomach cancer among people working at night

A very weak trend toward a slightly higher risk of stomach cancer among people working at night compared to no night work in a very large meta-analysis of 57 observational studies²⁰⁴Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.
Slightly higher risk of digestive system cancer among people working the greatest number of night shifts, or in some studies any night shifts, compared to no night shifts in a very large meta-analysis of marginal quality of 57 observational studies²⁰⁵Liu W, Zhou Z, Dong D, Sun L, Zhang G. Sex differences in the association between night shift work and the risk of cancers: a meta-analysis of 57 articles. Disease Markers. 2018 Nov 26;2018:7925219.

Lung cancer: good evidence of lower risk of lung cancer among people working at night

Slightly lower risk of lung cancer among people working at night compared to no night work in a very large meta-analysis of 57 observational studies²⁰⁶Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.

Lymphoma: weak evidence of a slightly higher risk of non-Hodgkin lymphoma among people working at night in a combined analysis of studies

A weak trend toward a slightly higher risk of non-Hodgkin lymphoma among people working at night compared to no night work in a very large meta-analysis of 57 observational studies²⁰⁷Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.

Melanoma and other skin cancer: good evidence of lower risk of skin cancer among people working at night

Slightly lower risk of skin cancer among people working at night compared to no night work in a very large meta-analysis of 57 observational studies²⁰⁸Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.

Ovarian cancer: no evidence of an effect on risk of ovarian cancer among people working at night in a combined analysis of studies

No higher risk of ovarian cancer among people working at night compared to no night work in a very large meta-analysis of 57 observational studies²⁰⁹Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.

Pancreatic cancer: no evidence of an effect on risk of pancreatic cancer among people working at night in a combined analysis of studies

No evidence of an effect on risk of pancreatic cancer among people working at night compared to no night work in a very large meta-analysis of 57 observational studies²¹⁰Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.

Prostate cancer: preliminary (conflicting) evidence of higher risk of prostate cancer among people working at night

No evidence of an effect on risk of prostate cancer among people working night shifts compared to other people in a very large meta-analysis of 57 observational studies²¹¹Dun A, Zhao X et al. Association between night-shift work and cancer risk: updated systematic review and meta-analysis. Frontiers in Oncology 2020 Jun 23;10:1006.
23% higher risk of prostate cancer among people ever working night shifts compared to no shift work in a very large meta-analysis of 15 observational studies²¹²Gan Y, Li L et al. Association between shift work and risk of prostate cancer: a systematic review and meta-analysis of observational studies. Carcinogenesis. 2018 Feb 9;39(2):87-97.
Slightly higher risk of prostate cancer among people working the greatest number of night shifts, or in some studies any night shifts, compared to no night shifts in a very large meta-analysis of marginal quality of 57 observational studies²¹³Liu W, Zhou Z, Dong D, Sun L, Zhang G. Sex differences in the association between night shift work and the risk of cancers: a meta-analysis of 57 articles. Disease Markers. 2018 Nov 26;2018:7925219.

Body terrain factors

Good evidence of higher risk of impaired glucose tolerance and diabetes among people working at night

Higher risk of diabetes among women reporting shift work compared to no shift work, with risk increasing with more years of shift work, in two very large observational studies²¹⁴Pan A, Schernhammer ES, Sun Q, Hu FB. Rotating night shift work and risk of type 2 diabetes: two prospective cohort studies in women. PLoS Med. 2011 Dec;8(12):e1001141.
Higher risk of type 2 diabetes among people working night shifts, and increasing risk with more night shifts per month, compared to day workers in a very large observational study²¹⁵Vetter C, Dashti HS et al. Night shift work, genetic risk, and type 2 diabetes in the UK Biobank. Diabetes Care. 2018 Apr;41(4):762-769.
Increasing risk of increased body weight and diabetes among women with increasing years of rotating night-shift work in a large observational study²¹⁶Kroenke CH, Spiegelman D et al. Work characteristics and incidence of type 2 diabetes in women. American Journal of Epidemiology. 2007 Jan 15;165(2):175-83.
Higher marker of blood glucose and poor glycemic control (HbA1c) among people with type 2 diabetes working night shifts, whether static or rotating, compared to other people in a mid-sized observational study²¹⁷Manodpitipong A, Saetung S et al. Night-shift work is associated with poorer glycaemic control in patients with type 2 diabetes. Journal of Sleep Research. 2017 Dec;26(6):764-772.
Higher risk of metabolic syndrome during 5 years of follow up among female employees (mean age of 32.8 years) without metabolic syndrome at baseline working persistent rotating shifts compared to few or no rotating shifts in a mid-sized observational study²¹⁸Lin YC, Hsiao TJ, Chen PC. Persistent rotating shift-work exposure accelerates development of metabolic syndrome among middle-aged female employees: a five-year follow-up. Chronobiology International. 2009 May;26(4):740-55.

Sound

Sounds can be either pleasant or unpleasant. Noise is any sound that is loud or unpleasant or that causes disturbance. Evidence regarding nature-based sounds is described above in Nature.

Preliminary evidence of increased risk for anxiety among adults with increased exposure to traffic noise

Preliminary evidence of higher perception of gastroesophageal reflux disease symptoms among people exposed to noise

Pleasant sounds: modest evidence of faster stress-recovery processes in laboratory experiments and better self-reported health conditions among people listening to positive soundscapes

Faster stress-recovery processes in laboratory experiments and better self-reported health conditions among people listening to positive soundscapes (pleasant, calm, less annoying sounds) in a review of 7 experimental or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies²¹⁹Aletta F, Oberman T, Kang J. Associations between positive health-related effects and soundscapes perceptual constructs: a systematic review. International Journal of Environmental Research and Public Health. 2018 Oct 29;15(11):2392.

Noise

Preliminary evidence of increased risk for anxiety among adults with increased exposure to traffic noise

Preliminary evidence of higher perception of gastroesophageal reflux disease symptoms among people exposed to noise

12% increased risk of anxiety with each 10-decibel increase in residential road traffic noise among adults of varying health status in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of observational studies of very low quality²²⁰Dzhambov AM, Lercher P. Road traffic noise exposure and depression/anxiety: an updated systematic review and meta-analysis. International Journal of Environmental Research and Public Health. 2019 Oct 27;16(21):4134.
A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward higher risk of anxiety with each day or evening 10-decibel increase in traffic noise including road, train, and aircraft among adults, especially those with more severe anxiety, in a meta-analysis of observational studies of low to very low quality²²¹Lan Y, Roberts H, Kwan MP, Helbich M. Transportation noise exposure and anxiety: a systematic review and meta-analysis. Environmental Research. 2020 Dec;191:110118.
Faster perception, higher intensity rating, and acid perfusion sensitivity score of gastroesophageal reflux disease symptoms among people with heartburn exposed to noise (auditory stress) compared to a control condition in a small RCT²²²Fass R, Naliboff BD et al. The effect of auditory stress on perception of intraesophageal acid in patients with gastroesophageal reflux disease. Gastroenterology. 2008 Mar;134(3):696-705.

Viruses and bacteria

A few viruses are known to cause cancer and are responsible for about 20% of total human cancer cases worldwide.

Strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) of a higher risk of hepatocellular carcinoma among people with hepatitis B virus or hepatitis C virus

Strong evidence of a higher risk of stomach cancer, nasopharyngeal carcinoma, or several types of lymphoma among people with Epstein-Barr virus

Strong evidence of higher risk of cervical cancer and other ano-genital neoplasms or head and neck tumors among people with high-risk HPV strains

Strong evidence of higher risk of adult T-cell lymphoma among people with human T-lymphotropic virus type 1

Strong evidence of higher risk of Merkel cell carcinoma among people with Merkel cell polyomavirus

Strong evidence of higher risk of Kaposi’s sarcoma among people with human herpes virus 8

Good evidence of a higher risk stomach cancer among people with Helicobacter pylori infection

Cancer risk

Gastrointestinal cancer

Strong evidence of a higher risk of hepatocellular carcinoma among people with hepatitis B virus or hepatitis C virus

Strong evidence of a higher risk of stomach cancer among people with Epstein-Barr virus

Good evidence of a higher risk stomach cancer among people with Helicobacter pylori infection

Hepatitis B virus (HBV) and hepatitis C virus (HCV) cause approximately 80% of hepatocellular carcinoma (HCC), the most common cancer of the liver.²²³Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4.
Epstein-Barr virus accounts for nearly 10% of stomach (gastric) carcinomas.²²⁴Shinozaki-Ushiku A, Kunita A, Fukayama M. Update on Epstein-Barr virus and gastric cancer (review). International Journal of Oncology. 2015 Apr;46(4):1421-34.
256% higher risk stomach cancer among people with Helicobacter pylori infection compared to other people in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 68 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies²²⁵Poorolajal J, Moradi L, Mohammadi Y, Cheraghi Z, Gohari-Ensaf F. Risk factors for stomach cancer: a systematic review and meta-analysis. Epidemiology and Health. 2020;42:e2020004.

Gynecological cancer: strong evidence of higher risk of cervical cancer and other ano-genital neoplasms among people with high-risk HPV strains

High-risk HPV strains are the major causes of cervical cancer and other ano-genital neoplasms.²²⁶Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4.

Head, neck, and oral cancer

Strong evidence of higher risk of head and neck tumors among people with high-risk HPV strains

Strong evidence of higher risk of nasopharyngeal carcinoma among people with Epstein-Barr virus

High-risk HPV strains are the major causes of a significant proportion of head and neck tumors.²²⁷Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4.
Epstein-Barr virus (EBV) is associated with nasopharyngeal carcinoma.²²⁸Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4; Wong Y, Meehan MT, Burrows SR, Doolan DL, Miles JJ. Estimating the global burden of Epstein-Barr virus-related cancers. Journal of Cancer Research and Clinical Oncology. 2022 Jan;148(1):31-46.

Lymphoma

Strong evidence of higher risk of adult T-cell lymphoma among people with human T-lymphotropic virus type 1

Strong evidence of higher risk of several types of lymphoma among people with Epstein-Barr virus

Human T-lymphotropic virus type 1 (HTLV-1) is the causative agent of adult T-cell lymphoma.²²⁹Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4.
Epstein-Barr virus (EBV) is associated with Hodgkin’s lymphoma, Burkitt’s lymphoma, diffuse large B-cell lymphoma (DLBCL), and extranodal NK/T-cell lymphomas.²³⁰Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4; Wong Y, Meehan MT, Burrows SR, Doolan DL, Miles JJ. Estimating the global burden of Epstein-Barr virus-related cancers. Journal of Cancer Research and Clinical Oncology. 2022 Jan;148(1):31-46. .

Melanoma and other skin cancer: strong evidence of higher risk of Merkel cell carcinoma among people with Merkel cell polyomavirus

Merkel cell polyomavirus (MCPyV) causes Merkel cell carcinoma.²³¹Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4.

Sarcoma: strong evidence of higher risk of Kaposi’s sarcoma among people with human herpes virus 8

Human herpes virus 8 (HHV8) is responsible for Kaposi’s sarcoma often found in patients with acquired immunodeficiency syndrome (AIDS).²³²Luo GG, Ou JH. Oncogenic viruses and cancer. Virological Sinica. 2015 Apr;30(2):83-4.

Your body terrain

Immunity: human immunodeficiency virus (HIV) is spread through infected semen, vaginal fluids, blood, and breast milk. While it does not cause cancer directly, researchers believe it increases the risk of cancer by damaging the immune system, which reduces the body’s defenses against other cancer-causing viruses.²³³Blackburn K. 7 viruses that cause cancer. MD Anderson Cancer Center. August 2018. Viewed April 11, 2022.

Helpful links

Known and Probable Human Carcinogens ›

Hair Dyes and Cancer Risk ›

Cancer Is an Environmental
Problem ›

How do chemical exposures affect our health? ›

Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) ›

Chemicals and Cancer ›

Cancer FactFinder ›

What are environmental risk factors, and how can I avoid them? ›

Toxicant and Disease Database ›

Endocrine Disruption ›

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Nancy Hepp, MS

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Last update: September 20, 2024

Last full literature review: March 2022

CancerChoices provides information about integrative in cancer care, a patient-centered approach combining the best of conventional care, self care and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocial therapy, and acupuncture therapies and self-care lifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.

Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.

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Creating a Healing Environment

Eating Well

Moving More

Sharing Love and Support

Exploring What Matters Now

Managing Stress

Creating a Healing Environment

Sleeping Well

How can Creating a Healing Environment help you? What the research says

On this page

Exposures to nature

Time in Nature or Forest Bathing

Optimizing your body terrain

Managing side effects and promoting wellness

Reducing cancer risk

Exposures to light and other radiation

Exposures to chemicals and other substances

Other environmental exposures

Helpful links

Keep reading

Creating a Healing Environment

More Healing Practices

Eating Well

Moving More

Sharing Love and Support

Exploring What Matters Now

Managing Stress

Creating a Healing Environment

Sleeping Well

Authors

Nancy Hepp, MS

Maria Williams

Reviewer

Laura Pole, MSN, RN, OCNS

Learn more

Conventional Care

Melatonin

Mind-Body Therapies: Introduction