Can Pesticides Cause Cancer?

Some pesticides cause cancer in humans, but the risk depends on the pesticide and the exposure. They do it through genotoxicity, endocrine disruption and epigenetic change. Regulators sort pesticides by cancer hazard first, and that step starts risk assessment. Blood cancers and solid tumors are the adult cancers linked to exposure, and childhood cancers add brain tumors. Licensed applicators, farmers, farmworkers and landscapers face the most risk. The evidence is mixed, because exposure assessment limits many studies. For food, residues at permitted levels are unlikely to cause cancer, and regulators set use limits before approval.

Do Pesticides Cause Cancer in Humans?

It depends. Some pesticides cause cancer in humans, but the risk depends on the pesticide and the exposure. The Environmental Protection Agency says cancer risk depends on a chemical’s potency and the potential for human exposure. The agency judges risk from both the toxicity of the pesticide and the likelihood of exposure.

Human cancer results for pesticides as a group are indeterminate, because exposure over long periods is hard to measure accurately. A 2021 study by Carol J Burns found the epidemiologic data neither strong nor consistent. The data concerned a positive association between occupational pesticide exposure and cancer. Several active ingredients were still associated with specific cancers.

IARC placed glyphosate, malathion and diazinon in Group 2A as probably carcinogenic to humans. Malathion is one of the oldest and most widely used organophosphate insecticides. The 2015 evaluation covered 5 organophosphate pesticides, with 3 in Group 2A and 2 in Group 2B.

Arsenic is a well established human carcinogen, with lung, bladder and skin tumors as its primary cancers.

Why Do Agencies Disagree About Pesticide Cancer Risk?

Agencies disagree about pesticide cancer risk because they ask different questions. The International Agency for Research on Cancer asks whether a chemical can cause cancer under any conditions. The Environmental Protection Agency asks about risk under expected real-world exposures. A hazard classification shows the strength of evidence, not the likelihood that cancer will occur at a given exposure level.

IARC reviewed about 1000 studies of glyphosate. Its Working Group weighs epidemiological evidence, animal bioassays and mechanistic data to judge carcinogenic hazard. IARC systematically assembles evidence from the public domain. Many regulatory agencies rely primarily on industry data that are not publicly available.

Genotoxicity splits the verdicts on diazinon, glyphosate and malathion. IARC found genotoxic potential in the three compounds, while JMPR found no genotoxicity. JMPR judged all three unlikely to cause cancer through dietary exposure.

The European Food Safety Authority reviewed the IARC report that classified glyphosate as probably carcinogenic to humans. A 2018 study by Peter Clausing argued that not classifying glyphosate as a carcinogen looks inconsistent with European weight-of-evidence guidance. A study by Pierluigi Cocco from the University of Manchester points to a second split. The European Union ended the license of mancozeb in January 2021. IARC placed EBDC fungicides in Group 3.

How Are Pesticides Classified for Cancer Risk?

Pesticides are classified for cancer risk through hazard identification, the first step of risk assessment. The IARC Monographs Programme runs the best known system, with groups from 1 to 4. A Working Group combines its conclusions into a consensus evaluation and sorts each agent into one of 4 categories. The categories range from Group 1, carcinogenic to humans, to Group 3, not classifiable as to its carcinogenicity to humans.

Group 2A means probably carcinogenic, and Group 2B means possibly carcinogenic. The programme has evaluated more than 1000 agents since 1971. A 1997 study by J Dich from Karolinska University Hospital notes IARC classified arsenic compounds and occupational insecticides as carcinogens.

The Environmental Protection Agency uses its own wording under the 2005 Guidelines for Carcinogen Risk Assessment. The descriptors are carcinogenic to humans, likely to be carcinogenic, suggestive evidence, inadequate information and not likely to be carcinogenic. Each descriptor applies under its own evidence condition, from strong human data to a lack of useful data. The agency updated these guidelines over the years to reflect a better understanding of how chemicals may cause cancer.

Which Pesticides Has IARC Classified as Carcinogens?

IARC Monographs Volume 112 has classified 5 pesticides as carcinogens, 3 in Group 2A and 2 in Group 2B. Key types include:

Glyphosate: A herbicide placed in Group 2A as probably carcinogenic to humans. It sits with malathion and diazinon in the higher group, so its rating rests on human, animal and mechanistic evidence.
Malathion: An insecticide placed in Group 2A as probably carcinogenic. The human evidence is limited for non-Hodgkin lymphoma and prostate cancer, and exposure of the general population is low.
Diazinon: An insecticide placed in Group 2A on limited human evidence for non-Hodgkin lymphoma and lung cancer. Strong evidence of DNA or chromosomal damage supports the rating, and most uses have been restricted in the USA, Canada and the European Union since the 1980s.
Tetrachlorvinphos: An insecticide placed in Group 2B as possibly carcinogenic on convincing evidence from laboratory animals. It kills fleas and ticks, and it is banned in the European Union but still used on livestock and companion animals in the USA.
Parathion: An insecticide placed in Group 2B as possibly carcinogenic on convincing evidence from laboratory animals. The rating rests on animal data rather than human data.

A Working Group of 17 experts from 11 countries met on 3 to 10 March 2015 to make these evaluations. A 2024 study by Parisa Sadighara of Tehran University of Medical Sciences tied about 13 food pesticides to carcinogenic effects. Glyphosate, tetrachlorvinphos, parathion, malathion and diazinon were among them, and most of the 13 were organochlorines.

How Does EPA Evaluate Pesticides for Carcinogenic Potential?

The Environmental Protection Agency evaluates pesticides for carcinogenic potential through the Office of Pesticide Programs. Its Health Effects Division reviews mouse and rat studies independently. The Cancer Assessment Review Committee peer-reviews those results and recommends a cancer classification. That classification determines how the agency regulates the pesticide.

Required studies cover 2 species, mice and rats, and both sexes for all pesticides used on food. The agency weighs how strongly carcinogenic a chemical is together with the potential for human exposure. It uses a weight-of-the-evidence review of all available studies. Carol J Burns concluded in 2021 that animal outcomes did not match human findings.

The 2005 final Guidelines for Carcinogen Risk Assessment replaced the 1986 guidelines and the 1999 interim final guidelines. Each system refers to its own criteria, so an older designation cannot be directly compared with a newer one. The review can repeat at reregistration, when new studies may lead the agency to re-evaluate the classification.

Which Cancers Are Linked to Pesticide Exposure?

Adult cancers linked to pesticide exposure include blood cancers and solid tumors, and childhood cancers add brain tumors. Key types include:

Non-Hodgkin lymphoma: A group of blood cancers that includes all lymphomas except Hodgkin lymphomas. It was noted in most adult studies, although the evidence for causation is limited.
Leukemia: A blood cancer that appears in adult and childhood studies. It was noted in most adult studies alongside non-Hodgkin lymphoma.
Prostate cancer: A solid tumor that shows associations with high occupational exposure. Solid tumors of the prostate, pancreas, kidney and breast were among the more consistent adult findings.
Kidney cancer: A cancer that appears mainly as renal cell carcinoma in occupational studies. A review of 4 studies of renal cancer after occupational exposure found a positive association in each.
Childhood brain tumors: Tumors that follow parental exposure. Leukemia and brain tumors are the childhood cancers with the most compelling evidence of association with pesticides.
Lung cancer: A cancer observed most often among pesticide applicators. Multiple myeloma and colon cancer follow it.

Lung cancer led the findings in a 2021 study by Jean V Varghese from Nirmala College of Pharmacy. That review covered 32 studies of pesticide applicators. Multiple myeloma is a malignancy affecting differentiated B lymphocytes.

A nationwide US population study found the strongest associations with pesticide use for non-Hodgkin lymphoma, leukemia and bladder cancer. Many adult studies are conducted in the occupational setting, so the evidence concentrates on workers. For children, parental exposure at work drives the findings.

IARC classifies 2,4-D as a possible carcinogen to humans, while the Environmental Protection Agency does not.

Can Pesticides Cause Non-Hodgkin Lymphoma?

Yes. Pesticides cause non-Hodgkin lymphoma in many studies, although IARC classed the human evidence for glyphosate as limited. Of 27 non-Hodgkin lymphoma studies meeting quality criteria in the Bassil review, 23 found positive associations. Non-Hodgkin lymphoma is a group of blood cancers that includes all lymphomas except Hodgkin lymphomas.

A 2014 study by Leah Schinasi pooled meta-analyses of 44 papers. Phenoxy herbicides, carbamate insecticides, organophosphorus insecticides and the organochlorine insecticide lindane were positively associated with the disease.

Exposure for longer than 10 years increased the risk for all hematopoietic cancers. Studies of different glyphosate formulations in different regions at different times reported similar increases in non-Hodgkin lymphoma.

The InterLymph Consortium was launched to pool data across studies in order to overcome the limits of single cohorts. The Agricultural Health Study, for example, followed people for a short period, which limits its ability to detect an association.

Can Pesticides Cause Leukemia?

Yes. Pesticides cause childhood leukemia, and acute lymphoblastic leukemia shows the strongest link with parental exposure at work. A study by Donald T Wigle from the University of Ottawa examined childhood leukemia and parental occupational pesticide exposure.

Thirteen of 18 studies in the 1998 Zahm and Ward review found increased leukemia risk after pesticide exposure. Maternal exposure to insecticides and paternal occupational exposure appear to carry the greatest childhood cancer risk. Early studies mixed leukemia types and were limited by recall bias.

Diazinon carries an adult leukemia signal. The Agricultural Health Study showed a risk of developing leukemia after exposure to diazinon. That study began in 1993 to answer how agricultural, lifestyle and genetic factors affect the health of farming populations.

Can Pesticides Cause Prostate Cancer?

It depends. Pesticides cause prostate cancer at high occupational exposure, but the association is weak and reviewers disagree on causation. All eight prostate studies in the Bassil review showed positive associations with pesticide exposure. A 2016 study by Anne-Mary Lewis-Mikhael examined occupational pesticide exposure and prostate cancer in a meta-analysis.

A review of 13 studies concluded there was no causal link between pesticides and prostate cancer. Epidemiological evidence did not support positive associations between DDT blood concentration and prostate cancer risk. A particularly well designed Agricultural Health cohort study included 55,000 men in Iowa and North Carolina. In the Agricultural Health Study, the highest-exposure applicators had an estimate reported for methyl bromide.

Prostate cancer is the uncontrolled growth of cells in the prostate, a gland below the bladder. IARC found limited evidence in humans linking malathion to prostate cancer. The association may relate to hormonally active pesticides, known as endocrine disruptors.

Does Glyphosate Cause Cancer?

It depends. Glyphosate causes cancer as a hazard under the IARC classification. The Environmental Protection Agency found no cancer risk under real-world exposure. The agency concluded in 2017 that glyphosate is not likely to be carcinogenic to humans. That assessment found no risks of concern from ingesting food with glyphosate residues.

IARC classified glyphosate in Group 2A on limited human evidence. It found sufficient evidence in experimental animals and strong evidence of genotoxicity for pure glyphosate and glyphosate formulations.

The Agricultural Health Study reported that no association was apparent between glyphosate and any solid tumors or lymphoid malignancies overall. Many glyphosate studies rely on self-reporting to determine exposure. IARC’s combined analysis of the Agricultural Health Study and all case-control studies showed a statistically significant association with non-Hodgkin lymphoma.

Roundup contains the isopropylamine salt of glyphosate as its main active ingredient. A study by Luoping Zhang from the University of California Berkeley used the highest exposure groups in each glyphosate study.

Registration review keeps the question open, because every pesticide goes through the same basic process. The agency is updating its evaluation of glyphosate’s potential to cause cancer. It can take prompt regulatory action at any time if new evidence indicates a safety concern.

How Do Pesticides Cause Cancer?

Pesticides cause cancer through genotoxicity, endocrine disruption and epigenetic change. Glyphosate caused DNA and chromosomal damage in human cells, though it gave negative results in bacterial tests. Malathion caused DNA and chromosomal damage and disrupted hormone pathways.

Endocrine disruption acts through nuclear receptor interaction, disturbed receptor signaling and changed hormone availability. The Food Quality Protection Act of 1996 first directed the Environmental Protection Agency to screen and test for endocrine disruption.

Arsenic exposure can cause epigenetic dysregulation, including DNA methylation, histone modification and microRNA expression. That dysregulation may play a mechanistic role in cancer development, though long-term studies have not yet confirmed this.

IARC reported statistically significant trends of more cancers at higher doses of pure glyphosate in mice. Those mouse studies showed unusual, rarely seen tumor types. A 2019 study by Luoping Zhang paired a meta-analysis of glyphosate-based herbicides with supporting evidence.

Those most at risk of pesticide-related cancer are licensed pesticide applicators, farmers and farmworkers, and landscapers. Pesticide manufacturing workers, children of exposed parents and residents of heavily farmed regions follow. The Agricultural Health Study follows more than 89,000 licensed applicators and spouses in Iowa and North Carolina.

Jean V Varghese titled a systematic review Pesticide applicators and cancer and reported lung cancer most often across 32 studies. Prostate cancer, multiple myeloma and colon cancer followed among applicators.

Farmers, pesticide applicators, landscapers and pesticide manufacturing workers are the adult occupational groups studied for non-Hodgkin lymphoma. The National Institute for Occupational Safety and Health is the federal agency for research on work-related injury and illness.

Children carry risk through their parents. Maternal insecticide exposure and paternal occupational exposure appear to carry the greatest childhood cancer risk. In regions with more crop growing, such as the Midwest, associations between pesticides and cancer incidence were more striking. Exposure beyond 10 years raised the hematopoietic cancer risk, as noted above.

How Much Does Prenatal Pesticide Exposure Raise Childhood Leukemia Risk?

Prenatal pesticide exposure raises childhood leukemia risk by an amount that 19 meta-analyses leave inconclusive. The CHAMACOS Study is the longest running birth cohort study of pesticides among children in a farmworker community. A 2022 study by Sehar Iqbal of the Medical University of Vienna reviewed 19 meta-analyses of childhood leukaemia.

A 2021 study by Maria A Karalexi found the evidence inconclusive. Estimates differ between meta-analyses, because evidence is limited by heterogeneous exposure assessment and multiple statistical testing. Effects are reported as summary estimates with confidence intervals. Residential herbicide exposure during childhood showed no association with childhood leukemia.

Do Pesticide Residues on Food Cause Cancer?

It depends. Dietary exposure to pesticide residues on food is unlikely to cause cancer at permitted levels. JMPR found diazinon, glyphosate and malathion unlikely to cause cancer in people through dietary exposure, based on a weight-of-evidence approach.

Acceptable daily intakes are used to set maximum residue limits for pesticides in food. The Codex Alimentarius Commission recommends many of these limits, and governments often follow them. Authorities enforce the limits so that lifetime food exposure will not have adverse health effects.

Genotoxicity does not explain dietary risk, because no pesticide authorized for food in international trade is genotoxic. The Environmental Protection Agency requires reasonable certainty of no harm from pesticide residues allowed to remain on food.

Parisa Sadighara titled a systematic review Residues of carcinogenic pesticides in food. It selected 26 manuscripts from 663 and linked about 13 pesticides to carcinogenic effects. Carcinogenic organochlorines in foods of animal origin sometimes exceeded permissible levels.

A 2020 study by Paweł Glibowski tied regular organic food intake to lower non-Hodgkin lymphoma risk in women.

How Strong Is the Evidence Linking Pesticides to Cancer?

The evidence linking pesticides to cancer is mixed, and exposure assessment limits many studies. A study by J Dich in Cancer causes and control found few, if any, associations that are established and causal. Cigarette smoking and infections carry much greater proportions of the cancer burden than environmental pollutants.

Adult studies share a recurring weakness: confirming whether exposure occurred and how much occurred. Many glyphosate studies rely on self-reporting, and other chemicals can confound the results. Population-level assessments may not reflect individual outcomes.

A 2012 study by Scott Weichenthal says exposure misclassification is a concern in the Agricultural Health Study. It may limit analysis of exposure-response. Over 1,600 farmers and applicators joined the Biomarkers of Exposure and Effect in Agriculture study to address this gap.

A study by Carol J Burns appeared in International archives of occupational and environmental health. Toxicology in laboratory animals did not reveal cancer outcomes concordant with epidemiologic findings in that study.

How Do Regulators Limit Pesticide Cancer Risk?

Regulators limit pesticide cancer risk through use limits that the United States Environmental Protection Agency sets before approval. The agency sets limits on how a pesticide may be used and how often. It fixes what protective clothing or equipment is required. Residue limits then apply after approval.

The Federal Insecticide, Fungicide, and Rodenticide Act authorizes the agency to regulate the distribution, sale, production and use of pesticides. The Worker Protection Standard aims to reduce pesticide poisonings and injuries among agricultural workers and pesticide handlers. Cumulative risk assessment covers groups of pesticides with a common toxic effect.

The Food Quality Protection Act of 1996 required reassessment of tolerances by August 2006. Tolerances rest on a risk assessment of aggregate exposure, cumulative effects, susceptibility of infants and children, and endocrine effects. USDA enforces tolerances for meat, poultry and some egg products, and FDA enforces them for other foods.

15 years is the longest gap allowed between reviews of a pesticide registration. Cancer classification may be re-evaluated at reregistration. A 2025 study by Mehrnoosh Abtahi found that 58% of pesticide-food pairs lacked Codex maximum residue levels. Another 34% had levels below the limits and 8% exceeded them.