Breast cancer is the second most common cancer diagnosis among women and cases are on the rise. Anyone can get breast cancer – but it’s most common in women.
A new peer-reviewed study looks at where Americans are exposed to chemicals that may contribute to that rise. Published in Environmental Health Perspectives, the analysis found that hundreds of chemicals tied to breast cancer risk in animal and laboratory studies turn up in everyday products, food, drinking water, pesticides and air pollution.
It was led by scientists at the Silent Spring Institute, with co-authors from the University of California, Berkeley, and the University of California, San Francisco.
In this study, the researchers found breast-cancer-relevant chemicals in consumer products, food, drinking water and drinking water supplies, pesticide products, medications and building materials.
Many of the chemicals are produced in large amounts. In 2019 alone, 143 were made in or imported to the U.S. in volumes of 1 million pounds or more.
A 2024 analysis by the same authors identified 920 chemicals that caused mammary gland tumors in animal studies or changed hormone activity in ways linked to breast cancer. This study tells us where we could potentially be exposed to those chemicals.
Breast-cancer-relevant chemicals
In their 2024 study, the Silent Spring researchers created the list of 920 chemicals they call breast-cancer-relevant chemicals. A chemical made the list if it did at least one of the following:
- Caused mammary gland tumors in rats or mice in at least one study.
- Increased estrogen or progesterone production in lab tests using human cells.
- Activated the estrogen receptor, the switch inside cells that responds to estrogen.
The researchers also checked whether each chemical can damage DNA, another way chemicals can lead to cancer. Many chemicals on the list do more than one of these things. Chemicals with strong hormone effects that also damage DNA were the most likely to cause mammary tumors in animals.
Presence on this list is not proof that a chemical causes breast cancer in people. It flags chemicals that need more research, especially when many of us are exposed to them every day.
What the authors found
The team combined data from more than a dozen federal databases that track how chemicals are produced, used, released into the environment and measured in people.
Some of the chemicals are well known, including bisphenol A, better known as BPA, bis(2-ethylhexyl) phthalate, the solvent dichloromethane and parabens. Others, such as p-cresol and 2,4-dimethylphenol, have received much less attention.
Federal biomonitoring data show many of these chemicals, or the compounds they break down into, are in almost all people. The “breakdown products” of methylparaben, the sunscreen active ingredient oxybenzone, several phthalates and certain pesticides were detected in more than 95% of people tested.
Industrial facilities reported releasing nearly 82 million pounds of these chemicals into the air, water and land in 2024. When the researchers included all sources of air pollution, such as vehicles, wildfires and the burning of fossil fuels, estimated emissions topped 2 billion pounds in 2020.
Consumer products
Most of the breast cancer chemicals, about 500, were present in the consumer products category. Of those, 181 are also hormone disruptors and 88 are genotoxic, meaning they can damage cellular genetic material, which can lead to mutations or cancer.
Among these commonly used ingredients in personal care products are chemicals like parabens, phthalates and bisphenols.
Also on the list are ingredients in hair dyes like resorcinol and p-phenylenediamine, which causes mammary tumors in animal studies. They can also damage DNA and increase production of estrogen and progesterone in lab tests.
Studies have linked hair dye use to breast cancer risk.
Prescription skin-lightening creams can contain hydroquinone, which also increased estrogen and progesterone production in lab tests. The researchers note these products are more likely to be used by women of color, which could add to existing disparities in exposure.
Pesticide products
The study also highlighted pesticide products as an important source of exposure to breast cancer chemicals. People can be exposed to pesticides in multiple ways, including as residues on produce and in drinking water. Pesticides may also be found in products in the home, such as insect repellents, medical treatments and pest control.
The study reported 485 chemicals found in pesticide formulations. But the authors point out that only about one-third of them are currently registered with the Environmental Protection Agency as active ingredients.
In most cases, before a pesticide can be sold, the EPA requires extensive toxicity testing of its active ingredients, including long-term studies of whether they cause cancer.
The other chemicals are classified as inert ingredients – solvents, preservatives and other chemicals that help a product work. Inert ingredients do not require tests as stringent as those for active ingredients. Only sometimes they are required to be on product labels. This means people using these products usually can’t tell which inert ingredients they contain.
Using national biomonitoring data collected between 2017 and 2020, the study reported that organophosphate pesticides (like malathion, which is commonly used on crops) were found in more than 90% of the U.S. population.
This finding adds to existing concerns about widespread “forever chemicals” PFAS pesticide use, including mixtures of pesticide classes frequently detected on produce.
Food and water
The researchers report 462 of these chemicals in food. Of these, 83 are on the Food and Drug Administration’s list of substances added to food, which means they are expected to be there. The others may be present as contaminants that migrate from packaging and processing equipment or be present as contaminants for other reasons, such as pesticide residues.
Others are chemicals formed when meat is cooked at high temperatures and some, such as soy compounds, occur naturally in plants.
People who rely more on packaged and ultra-processed foods may face higher exposure to chemicals from food additives and packaging.
The authors also reported 162 breast-cancer-relevant chemicals, such as pesticides and industrial solvents, likely to be present in drinking water.
Some chemicals form as byproducts when drinking water is disinfected. These disinfection byproducts, or DBPs, emerge when disinfectants such as chlorine react with naturally occurring organic matter in water.
Some DBPs have been linked to cancer and other health concerns.
Among the pesticides linked to breast cancer and reported present in drinking water, 50 have current registrations, but 37 no longer have a current EPA registration.
The data source the authors used to identify chemicals in drinking water, the EPA’s CPDat, reports only whether a chemical has been found in drinking water. It does not report where or how much of it was found or when the detection occurred.
Pharmaceuticals
The researchers also found 142 breast-cancer-relevant chemicals in medications sold in the U.S. Most of the active ingredients fall into a few groups: hormone treatments, chemotherapy drugs, treatments for infections and parasites, anti-inflammatory drugs and blood pressure medications.
This does not mean you should stop taking medication. Many of these drugs treat serious conditions, and some, like hormone therapies, have been shown to interact with the hormone system because they have been designed for that purpose.
Totality of exposures
The study highlights the widespread occurrence of breast-cancer-relevant chemicals. People are not just exposed to one chemical at a time. They’re exposed to hundreds of chemicals from multiple sources over the course of their lives. Even if most are at low levels, exposures add up.
The national biomonitoring data cited in the study show how common these combined exposures are. Research shows that exposure to chemical mixtures, or multiple chemicals that can add up or sometimes interact together to multiply each other’s effects, creates a total health risk that is measurably more harmful than those from the chemicals acting alone.
And in most cases, regulations for chemicals do not take cumulative exposures into account.
What you can do to reduce exposure
- Check EWG’s resources for safer products. Use our Healthy Living App, Skin Deep® and Guide to Healthy Cleaning and look for products with low hazard scores or our EWG Verified® mark.
- Invest in a home water filter for improving water quality. Consult the EWG Tap Water Database to find out what’s in your water. EWG’s water filter guide can help you find the right filter for your budget. Shop organic, when possible, to reduce pesticide exposure. Consult the EWG Shopper’s Guide Pesticides in Produce™ to find out which fruits and vegetables have the highest and lowest pesticide residues, so you can make the best decisions for your family. And see EWG’s Guide to Washing Produce.
- If you have questions about a medication, especially if you have a history or higher risk of breast cancer, talk with your doctor or pharmacist before making changes.
Other actions you can take
- Know your family history. If possible, find out whether anyone in your family has had breast cancer. Some genes with mutations increase risk of developing this type of cancer.
- Get screened early. Preventive procedures such as regular breast cancer screenings are important to detect breast cancer early, which can also make it easier to treat. As of 2026, experts suggest screening for breast cancer starting at age 40.
