Mackenzie Varieur is a senior public health sciences student at the University of Massachusetts-Amherst. She is the Science Director for Protect Our Breasts (POB) an international organization dedicated to sharing the science behind chemicals of concern in everyday products while advocating for safer alternatives in the consumer marketplace.
To learn more about POB’s mission and latest work, go to Protect Our Breasts

Did you know that in the United States one in eight women will be diagnosed with breast cancer in their lifetime? This statistic has increased drastically from 1940 when the estimated risk was approximately one in twenty (Massachusetts Breast Cancer Coalition [MBC], 2020). Despite the popular misconception, only 5-10% of breast cancer cases are attributed to inherited genetic mutations, such as the BRCA1 or BRCA2 gene. With an estimated 15-25% of cases linked to lifestyle factors, this leaves up to 70% of breast cancers largely unexplained (MBC, 2020). Mounting evidence suggests that environmental factors, including chemicals in consumer products, may be linked to the development of breast cancer.

Protect Our Breasts is a nonprofit organization sharing the scientific evidence on these chemicals of concern, translated for high school and college-aged women in a “window of susceptibility.” One group of chemicals of focus, which has become of increasing concern, is **endocrine disrupting chemicals (EDCs).

Image Copyright: European Parliament

EDCs are a group of chemicals that affect the endocrine system. The endocrine system acts as the body’s communication system, with hormones, such as estrogen, acting as messengers that help to regulate essential functions such as reproductive development, fertility, behavior, and homeostasis. EDCs disrupt this communication system through blocking, mimicking, or altering the hormones naturally found in the body. These disruptions can lead to developmental changes within the body that may increase the risk of developing adverse health effects, such as breast cancer.

In regard to many carcinogenic chemicals, it is often believed that the dose of a chemical is approximately proportional to the response. This means that the higher the amount of the chemical that is found in the body, the greater the effect. Research has shown, however, that EDCs can cause effects within the body at low doses . This is because hormones typically work at very small doses within the body. For this reason, low levels of EDC exposure can in turn interfere with hormone production, regulation, and function (Gray et al., 2017).

The timing of exposure is also crucial and can influence whether, how much, and how exposure to an endocrine disrupting chemical might influence the risk of a later breast cancer diagnosis (Zoeller et al., 2015; Gray et al., 2017). Studies have illustrated that exposure to endocrine disruptors during development stages , typically at stages up through a woman’s first full-term pregnancy, can lead to health effects such as breast cancer later in life ( Rudel, Fenton, Ackerman, Euling, & Makris, 2011; Zoeller et al., 2015; Rodgers, Udesky, Rudel, & Brody, 2018). This has been often referred to as a “window of susceptibility.”

Two of the most well-known endocrine disrupting chemicals found in cosmetic and personal care products that have been linked to an increased risk for breast cancer are phthalates and parabens . Both chemicals have been identified as possessing estrogenic properties.

Phthalates are a group of chemicals known for their ability to make plastics more flexible, but they are also found in cosmetics and personal care products, especially those which contain fragrance. Several studies have illustrated links between phthalate exposure and breast cancer risk. For example, one epidemiological study found associations of high urinary concentrations of phthalates used in fragranced products, known as BBP (benzyl butyl phthalate), to be associated with a higher risk of breast cancer.

Another study observed that young girls who experienced early breast development who also had high levels of MMP (monomethyl phthalate) in their bodies were at increased risk for developing breast cancer. In multiple animal studies, phthalates such as BBP and DEHP (diethylhexyl phthalate) were found to have induced cell proliferation in mammary glands of rats, a key indicator of potential cancerous tumor development (Gray et al., 2017).

Parabens are another group of chemicals used as preservatives in makeup, skincare products, and other personal care products. Parabens have been found at measurable concentrations in biopsy samples of breast tumors, which is suggestive of their ubiquity in the body after using a cosmetic product. Additional studies illustrate the potential of parabens such as methyl-, propyl- and butyl-parabens to stimulate the growth of estrogen receptor positive breast cancer cells, highlighting a possible link between parabens and growth of hormone-receptor positive breast cancers. (Gray et al., 2017; Breastcancer.org, 2020).

Additionally, personal care products that contain sunscreen may contain endocrine disrupting chemicals as well, such as benzophenone-3 (commonly known as oxybenzone), homosalate (HMS), 3-(4-methylbenzylidene)-camphor (4-MBC), octyl-dimethyl-PABA (OD-PABA), and octyl-methoxycinnamate (also known as octinoxate). These are among the most commonly used sunscreen chemicals and have been shown to exhibit “significant estrogenic activity as measured by increased proliferation of human breast cancer cells” (Gray et al., 2017).

Thanks in part to greater research and general awareness, these chemicals and many more have been identified for their possible health risks. However, it cannot be declared that there are clear causal links between these chemicals and health issues such as breast cancer. This is due to the inability to study unexposed individuals and to the vast amount of literature being primarily focused on epidemiological associations or animal studies. Further research is still necessary to unequivocally establish their risk.

Until then, individuals should be cautious and aim to limit their exposure when possible by avoiding products that contain phthalates, parabens, and other EDCs. Above all else, staying informed on the latest research is essential in understanding the role that these chemicals and other environmental factors play in affecting our health.

Sources

• Breast Cancer Prevention Partnership [BCPP]. (2019, July 17). BCPP behind the science: Episode 2 endocrine disruptors with
• Sarah Janssen, MD, PhD, MPH [Video]. YouTube. https://www.youtube.com/watch?v=P-xwZOPmf-0 . Breastcancer.org. (2020, September 11) “Exposure to chemicals in cosmetic products.” Retrieved from https://www.breastcancer.org/risk/factors/cosmetics .
• Gray, et al. (2017). “State of the evidence 2017: an update on the connection between breast cancer and the environment.” Environmental Health , 16(94). Doi: 10.1186/s12940-017-0287-4.
• Massachusetts Breast Cancer Coalition [MBCC]. (2020). “Breast cancer and the environment.” Retrieved from https://mbcc.org/breast-cancer-prevention/be-informed/breast-cancer-and-the-environment/ .
• National Research Council. (2014). “Review of the Environmental Protection Agency's state-of-the-science evaluation of nonmonotonic dose-response relationships as they apply to endocrine disruptors.” Washington, DC: The National Academies Press. https://doi.org/10.17226/18608 .
• Rodgers, K., Udesky, J., Rudel, R., & Brody, J. (2018).“Environmental chemicals and breast cancer: An updated review of epidemiological literature informed by biological mechanisms.” Environmental Research, 160. pp. 152-182. https://doi.org/10.1016/j.envres.2017.08.045 .
• Rudel, R., Fenton, S., Ackerman, J., Euling, S., & Makris, S. (2011). “Environmental exposures and mammary gland development: state of the science, public health implications, and research recommendations.” Environmental Health Perspectives , 119 (8), pp. 1053–1061. https://doi.org/10.1289/ehp.1002864 .
• Zoeller, R.T., Bergman, Å., Becher, G., et al. (2014). “A path forward in the debate over health impacts of endocrine disrupting chemicals.” Environmental Health, 13( 118). https://doi.org/10.1186/1476-069X-13-118 .