A new report by researchers at the National Institutes of Health, or NIH, links chemicals commonly used in hair dyes and chemical hair straighteners to an increased risk of breast cancer.
The study, published last week in the International Journal of Cancer, found that participants who regularly used permanent hair dye in the year before the study’s start were 9 percent more likely to develop breast cancer than women who did not use it. But the risk from permanent dye was more than six times greater in black women than in white women who participated in the study.
“Researchers have been studying the possible link between hair dye and cancer for a long time, but results have been inconsistent,” corresponding author Alexandra White, Ph.D., of the National Institute of Environmental Health Sciences, part of the NIH, said in a press release. “In our study, we see a higher breast cancer risk associated with hair dye use, and the effect is stronger in African American women, particularly those who are frequent users.”
Black women participants who used permanent dye were associated with a 45 percent higher breast cancer risk, compared to a 7 percent higher risk in white women participants.
Study participants who used chemical straighteners every five to eight weeks had a 31 percent higher associated breast cancer risk than women who did not use chemical straighteners as frequently. But there was no notable difference between black and white participants.
The researchers assessed data, including information about health and lifestyle habits and personal care product use, from more than 46,000 U.S. women ages 35 to 74 who participated in the NIH’S Sister Study. All study participants had at least one sister with breast cancer, but the participants themselves did not have a history or diagnosis of breast cancer at the start of the study.
It’s important to note that the study results do not definitively mean that these hair products cause breast cancer. Many factors contribute to breast cancer development, including environment, lifestyle and family history. But the association seen in the study adds to the body of evidence that these products may be harmful.
- p-phenylenediamine, a common ingredient in hair dyes, is a strong skin sensitizer and has been shown to induce tumors in the mammary gland of rats.
- Resorcinol, used in hair dyes, can affect the proper functioning of hormones and trigger allergic reactions.
- Formaldehyde, used in high concentrations in certain keratin hair straighteners, is a known human carcinogen.
In addition, many hair relaxers contain caustic ingredients like sodium hydroxide. And some researchers have suggested that aromatic amines in hair dyes have endocrine-disrupting properties and may contribute to cancer.
Although the disparity in the risk to black women versus white women seen in the NIH study is shocking, it’s not surprising.
Researchers have found that certain hair care products marketed to black women, including hair dyes and chemical straighteners, contain many endocrine-disrupting chemicals that may contribute to the higher associations of breast cancer. A 2016 EWG study of personal care products marketed to black women also found that fewer than one-fourth of the products marketed to this demographic were “clean” or had fewer potentially hazardous ingredients, compared to the products marketed to the general public.
Given the latest evidence linking these products to serious health harms, EWG recommends avoiding or limiting the use of chemical hair straighteners and hair dyes as much as possible. You may also consider using resources like EWG’s Skin Deep® cosmetics database, a free online resource that rates more than 70,000 personal care products based on the hazards associated with their ingredients, and our Healthy Living App, to find heathier hair care products that do not contain carcinogens and other ingredients of concern.