Common Chemicals: Breast Cancer Link?

Every day, we encounter hundreds of chemicals from a wide variety of sources — the food we eat, the air we breathe, the water we drink, the personal products we use, and other items we touch and use at work, school, and in our homes. 

Some of these common chemicals may contribute to an increased risk of breast cancer, researchers say. But it’s hard to know exactly how much of a difference they make in your risk. 

No chemicals in personal care products that are currently on the market have been proven to cause breast cancer. But some people, including researchers, are concerned that there might be risks that are hard to confirm.

If you’re concerned in particular about antiperspirants, the American Cancer Society’s website states that there are “no strong epidemiological studies in the medical literature that link breast cancer risk and antiperspirant use, and very little scientific evidence to support this claim.” A study done in 2002 largely debunked rumors about antiperspirants and breast cancer risk. 

However, there have been certain chemicals – no longer in use in the U.S. – that were proven to raise your risk of breast cancer. These included the pesticide DDT (which is banned in the U.S.) and a form of estrogen called DES (diethylstilbestrol) which was often given to pregnant women between 1938 and 1971. It, too, has long been out of use in the U.S. 

A wide range of chemicals today are being studied because they have been shown to raise estrogen levels. Higher estrogen levels are known to raise breast cancer risk in women. So researchers want to learn whether any chemicals directly raise breast cancer risk in people – and if so, which chemicals pose the greatest risk and at what level of exposure.

So far, none of these chemicals have been shown to directly cause breast cancer in people.

As we learn more about cancer, including how it starts and grows, researchers are exploring all the ways these chemicals in our daily life affect our bodies and may contribute to the disease. 

“We’re always interacting with the chemicals around us and in our bodies,” says Ruthann Rudel, the lead researcher exploring the exposure and toxicology influence on breast cancer at Silent Spring Institute, a national environmental health research organization. She notes that some chemicals might damage DNA or affect hormone levels. “Our body will resolve some of those things some of the time,” Rudel says. But the concern, she says, is that “every exposure just increases the risk a little bit.”

When looking into chemicals and how they impact cancer or increase your risk of cancer, these are some of the things that researchers consider:

The chemicals you were exposed to and their short-term and long-term effects. Your level of exposure. Were you exposed to each chemical just once or over a long time? Even small exposures can add up over a lifetime. When you were exposed to these chemicals. Certain times in your life may be more vulnerable, including when you were in utero and as an infant, young child, and teen (especially during puberty).The mixture of chemicals at the time of exposure. Some chemicals aren’t a risk when you are exposed to them alone. But some chemicals in combination together may be of more concern.How long the chemicals stay in your body. The longer they stick around, the more of an issue they may be.

Finding out exactly which chemicals might influence the development or growth of breast cancer is challenging for a variety of reasons.

First, researchers cannot test them directly in people. But they can look for possible associations between chemical exposure and breast cancer risk.

“It’s difficult to find any association between exposure and cancer because you need a large group of people, you need to know what their exposure was, you need to have a variation in exposure – some people high, some people low – and you need to follow them for 20 or 50 years and figure out if they got cancer or not,” Rudel says. “And you need to do that for thousands of people. So that is expensive and almost impossible most of the time.”

Chemicals can also be studied in labs, with tests done on human cells or in mice or other animals. However, that’s not a perfect substitute for what happens in people. 

Another complication is the fact that nearly everyone is exposed to many chemicals.

“We’re kind of getting hit from all over the place by a variety of different chemicals,” including those that directly affect genes and those that disrupt our endocrine (hormone) system, says Janet Gray, PhD, professor emeritus at Vassar College. She’s researched the link between chemicals and breast cancer for more than two decades. 

“Many of the chemicals we’re so worried about, we have a hard time studying in people,” Gray says. “It’s very hard to study if 95% of us have this chemical in our body.”

Add in the different mixtures of chemicals we’re exposed to and at different times in our lives, and you can see how complicated it can be to pinpoint which chemicals may raise your risk of breast cancer.

“We’re not exposed to one chemical at a time,” Gray says. “We are exposed through the air, through where we and especially where our children play, through the water we drink, etc.” She points out that the chemicals can also interact. “Sometimes they counterbalance each other,but more often they increase the whammy of the exposure, so to speak.”

Research into chemicals and breast cancer has come a long way, Gray says, partly due to the studies that showed how exposure to DDT and DES increased the risk of the disease.  Studies on DES showed that limited exposure during a critical time in development could raise a woman’s risk of breast cancer. 

“For the girls who were exposed in utero to DES, once they were born, they were no longer exposed,” Gray says. “Their moms had taken it while they were pregnant … and then [had] no more exposure. And still, they have a higher risk of breast cancer.” 

Endocrine disruption compounds (EDCs) are among the many types of chemicals that researchers are studying. They’re looking at how EDCs may interfere with the endocrine system and hormones that control many functions in the body.

EDCs are of particular concern with breast cancer risk because increased levels of hormones including estrogen or progesterone are known to raise the risk and growth of breast cancer.  About 3 in 4 breast cancers rely on these hormones to grow. 

“We are being exposed to chemicals that work on a system that is altered by these exquisitely low exposures, whether it’s to natural hormones or these environmental chemicals,” Gray says.

One EDC chemical that has been linked to breast cancer is bisphenol A, also known as BPA, which can be found in some plastics and has been associated with other health concerns, as well. That research is mainly from lab studies, tests done on animals, or epidemiological studies which look for patterns among big groups of people. While BPA has been removed from many products, Gray and other researchers say it is often substituted with chemicals that affect the body in similar ways. 

“Unfortunately, [products] were BPA free, but the BPA had been substituted with bisphenol S or bisphenol F,” Gray says. “So very closely related chemicals that had the same effects on plasticizing, but were just as estrogenic, if not more so.”

Other EDC chemicals being studied include parabens (often used as artificial preservatives in cosmetics), and phthalates, among others. 

In 2021, Rudel and a colleague at Silent Spring reviewed data on more than 2,000 chemicals from the Environmental Protection Agency (EPA) ToxCast program. They looked to see if the chemicals raised the levels of estradiol — the strongest type of estrogen — and progesterone in human cells in a lab. They found 296 chemicals increased the two hormones and 71 increased both. However, the study did not look at whether that affected breast cancer risk or other health risks in people.

Rudel says she hopes the study will lead to further research.

It’s nearly impossible to avoid all chemicals. But if you’re concerned about your exposure, you can do things to limit that. 

“Don’t be scared and don’t give up hope,” Gray said. “But that said, really try as much as possible for yourself and your families at home, at school, at work, to use as few chemicals and avoid plastic as much as possible.”

Suggestions from Gray and Breast Cancer Prevention Partners include:

Don’t store food in plastic containers.Don’t heat food in the microwave in plastic. Avoid or lessen the use of pesticides on your lawn.Avoid products with fragrances in them.Use or make simple cleaners.

Rudel suggests you can learn more tips on reducing chemical exposure via Silent Spring’s Detox Me app. She also encourages people to speak to lawmakers about the importance of regulation and testing on chemicals. 

“I try to tell people, don’t sweat every last thing, but just try to do the ones that are easy for you,” Rudel says. “And vote.”

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