Permanently coloring or straightening your hair can change your look and even boost your confidence in just hours. But both techniques use products that contain strong chemicals, which may make you wonder whether there are any health risks involved. In particular, can using hair dyes or relaxers impact your risk for cancer?
Here, learn more about how hair dyes and relaxers are used, which ingredients have been studied, and what the research says about their possible links to cancer.
What are hair relaxers and hair dyes?
A chemical hair straightener, also called a hair relaxer, is a chemical product that changes the structure of hair from curly to straight. Hair relaxers straighten the hair for several months at a time, and the hair even remains straight after getting wet. Hair relaxers can contain many different chemical components and come as different formulations, such as liquid keratin or thermal reconditioning.
A permanent hair dye strips the hair of its natural color and then imbues the strands with new colors. As the name suggests, this type of hair dye permanently changes the color of your hair. However, your natural color will begin to show at your roots in several weeks. Hair dyes can also contain many different chemical components, including bleach and/or peroxide.
What has research shown about hair dyes, hair relaxers, and possible cancer risk?
Past studies on hair dyes or relaxers and risk for links to cancer have often been inconsistent in their findings. In the past 5 years, several large studies in the United States have investigated the association between cancer and hair products. These studies have focused on cancers such as breast cancer, ovarian cancer, and uterine cancer, which can use the hormones estrogen and/or progesterone to grow.
None of these studies showed definitive proof that hair relaxers or dyes do or do not cause cancer. But, they did show a possible link between frequent use of chemical straighteners and breast, ovarian, and uterine cancers. This could be due to chemicals commonly found in these products, such as formaldehyde, formaldehyde-releasing chemicals, oxidized para-phenylenediamine, and 4-aminobiphenyl, which could potentially lead to cancer.
In a 2020 study in the International Journal of Cancer, researchers found that women who frequently used chemical hair straighteners, defined as more than 6 times a year, had about a 30% higher risk of breast cancer. Similarly, according to a 2021 study in Carcinogenesis and a 2022 study in the Journal of the National Cancer Institute, women who frequently used chemical hair straighteners, defined as more than 4 times a year, were twice as likely to develop ovarian cancer and more than twice as likely to develop uterine cancer as women who did not use chemical hair straighteners.
In these same studies, there was some evidence that permanent hair dye was also associated with increased breast cancer risk, particularly among Black women. However, there was no association found between hair dye and ovarian or uterine cancers.
A separate 2020 study in the British Medical Journal found a higher risk of ovarian and some breast cancers for women who had dyed their hair 100 times or more. That study did not, however, find a connection between permanent hair dye use and most other cancers, such as bladder, brain, colon, kidney, or lung cancers.
“Hair products such as dye and chemical straighteners or relaxers contain a number of chemicals that may act as carcinogens or endocrine disruptors, and thus may be important for cancer risk. Straighteners, in particular, have been found to include chemicals such as phthalates, parabens, cyclosiloxanes, and metals and may release formaldehyde when heated.” -- Alexandra White, PhD, MSPH, who leads the Environment and Cancer Epidemiology group at the National Institute of Environmental Health Sciences and has researched the link between hair products and cancer risk
Are certain groups of people at higher risk?
Black people use hair relaxers more frequently than other racial and ethnic groups, which could potentially put them at higher cancer risk. For example, one 2017 study found that 88% of Black women used chemical straighteners versus 5% of White women. “As Black women are the most frequent users of these products, these findings are more relevant and impactful for them,” says Dr. White. However, according to Dr. White, scientists need to better understand the range of hair products used across racial and ethnic groups and then study those products and the associated cancer risk in diverse populations.
Hairdressers are another group who may be at higher cancer risk from using these products. Their on-the-job risk of working daily with these types of products has been studied by the World Health Organization’s International Agency for Research on Cancer, which classifies working with hair dyes as a probable carcinogen.
What should people look out for when considering these hair products?
The U.S. Food and Drug Administration (FDA) regulates hair products but does not test products for safety, which is the responsibility of manufacturers. When considering products, the FDA’s website recommends reading the label to identify and avoid formaldehyde or its liquid forms, formalin and methylene glycol, as formaldehyde is a known carcinogen. A carcinogen is any substance that causes cancer. You can also ask your hairdresser about the ingredients in hair products they use.
If you are concerned about your individual cancer risk and how using certain hair products may impact it, talk with your doctor about your specific risk factors.