30 March, 2021

To celebrate Pesticide Action Week, Dr Robin Mesnage, a Research Associate at Kings College and member of Breast Cancer UK’s Scientific Review Panel investigates the links between pesticides and breast cancer risk.

What do we know about pesticides and breast cancer risk?

Whether pesticides have toxic effects and cause breast cancer is a burning question, both for the scientific community and for consumers who want to lead a healthy lifestyle.

What are pesticides and where they are used?

A pesticide can be a weedkiller used to clear invasive weeds in agriculture fields. It can also be a fungicide or an insecticide. Pesticides are not only sprayed in agricultural fields, but also in private or public gardens, on rail tracks, industrial sites, golf courses, or even on verges of most cities.

In a recent scientific study 1, grass samples from playgrounds and schoolyards in Italy were found to be contaminated by dozens of pesticides. Some of them are known endocrine disrupting chemicals, with harmful properties that raise questions about their potential role in breast cancer development.

Pesticides are generally linked to modern agriculture. Farmers who apply pesticides in their fields are often criticised by individuals or environmental organisations, causing growing resentment. This is sometimes known as ‘agribashing’. We should not neglect the challenges farmers are facing. The toxic effects of pesticides in farming communities are well known. The largest agricultural study conducted in the US has identified a link between the use of some insecticides and breast cancer risk among farmers’ wives 2.

Investigating the role of pesticide exposures in breast cancer development for women working on farms should be a priority. Women represent a large proportion of the agricultural workforce. Women may have greater risk of pesticide exposure than men, as suggested in a study of Latina farmworkers in the US 3. It was found that women are often less protected than men when they handle pesticides, because they have difficulty accessing properly fitting personal protective equipment which is typically designed for men.

What about consumers?

Consuming fruits and vegetables grown on organic farms will certainty reduce an individual’s pesticide exposure. This is not very surprising. However, some major sources of pesticide exposure are closer to home. An inconvenient truth is that large quantities of insecticides are bought to kill mosquitoes, clothes moths, or other inconvenient bugs.When blood or urine tests reveal an exposure to a dangerous dose of pesticide, the source is often domestic.

Let’s adopt a precautionary approach and avoid unnecessary toxic exposures.

Ask yourself, is this mosquito on the wall worth a pesticide exposure? Some flea and tick collars for dogs contain doses of insecticides sufficient to kill approximately 1 billion honey bees or a thousand partridges. The use of these collars is a major source of insecticide exposure 4. Ask yourself if your dog really needs it?

New clothes are also frequently contaminated by pesticides sprayed on cotton, or because they are included in protective treatments during manufacturing. Always wash new clothes before wearing them.

The issue of screening for pesticides

Another problem is that pesticide screening in blood or urine is almost never done. Even after decades of controversies surrounding the toxic effects of pesticides 5, it is still not clear whether exposures at low doses present in the environment can cause diseases.

The sources of exposures to pesticides are multiple and difficult to evaluate. We are exposed to different doses of pesticides at different moments of our lives. It is difficult to predict when toxic effects of pesticides can manifest. We studied the effects of glyphosate on breast cancer cells with the support of BCUK. This was an important study because of the debates surrounding glyphosate carcinogenicity, but we only scratched the surface as dozens of pesticides are used in the UK6.

The development of breast cancer can be initiated in the womb by toxic exposures, but these are only detected after a few decades.

This is an incredibly complex topic.

The most reliable strategy to evaluate the adverse effects of pesticides in human populations is not to conduct animal studies, or survey food for pesticide residues, but to directly measure pesticide exposure by blood or urine screening. One of the few surveys performed in the US showed that high blood levels of the banned insecticide DDT predicted a 5-fold increased risk of breast cancer 7. Despite the worrying signs from this study, the presence of pesticides in the UK population has never been evaluated. There is an urgent need for human monitoring of pesticides.

Pesticide exposures are difficult to avoid. However, there is a lot we can do to reduce risks. Small actions, such as seeking information, or reconsidering the use of toxic chemicals in your house, may have significant consequences!

Written by Dr Robin Mesnage, who is a Research Associate in the Department of Medical and Molecular Genetics at King’s College London. He is a computational toxicologist whose main research interest focuses on understanding the effects of pollution on human health. He is also a consultant, providing expert advice on the risk assessment of pesticides. He is also a member of Breast Cancer UK’s Independent Scientific Review Panel.

Twitter: @Robin_Mesnage

Breast Cancer UK does not endorse any products or any opinions expressed by our guest bloggers.  The blogs are the personal opinions and endorsements of the blogger and not necessarily reflective of Breast Cancer UK views.  If you have questions about the blog, please contact [email protected].


  1. Linhart C et al. (2021) Year-round pesticide contamination of public sites near intensively managed agricultural areas in South Tyrol. Environ Sci Eur 33, 1. https://enveurope.springeropen.com/articles/10.1186/s12302-020-00446-y
  2. Engel LS et al. (2017) Insecticide Use and Breast Cancer Risk among Farmers’ Wives in the Agricultural Health Study. Environ Health Perspect. 2017;125(9):097002. https://ehp.niehs.nih.gov/doi/10.1289/EHP1295?url_ver=Z39.88-2003
  3. Curl CL et al. (2021) Measurement of urinary pesticide biomarkers among Latina farmworkers in southwestern Idaho. J Expo Sci Environ Epidemiol. doi:10.1038/s41370-020-00285-2. https://www.nature.com/articles/s41370-020-00285-2
  4. Perkins R et al. (2021) Potential role of veterinary flea products in widespread pesticide contamination of English rivers. Sci Total Environ. 755(Pt 1):143560. https://www.sciencedirect.com/science/article/abs/pii/S0048969720370911
  5. Mesnage R and Zaller JG, eds. Herbicides: Chemistry, Efficacy, Toxicology, and Environmental Impacts. Elsevier in cooperation with RTI Press. ISBN: 9780128236741. https://www.elsevier.com/books/herbicides/mesnage/978-0-12-823674-1
  6. Mesnage , et al. (2017). Evaluation of estrogen receptor alpha activation by glyphosate-based herbicide constituents. Food Chem Toxicol. 2017 Oct;108(Pt A):30-42. https://www.sciencedirect.com/science/article/pii/S0278691517303976?via%3Dihub
  7. Cohn BA et al. (2015). DDT Exposure in Utero and Breast Cancer. J Clin Endocrinol Metab. 100(8):2865-72. https://academic.oup.com/jcem/article/100/8/2865/2836085

For information about pesticides and breast cancer risk see our EDC brief here and for Breast Cancer UK’s position on organic food see here

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