Research suggests that permanent hair dye and chemical hair straighteners could increase breast cancer risk, especially for black women.
The research was published online on Dec. 3, 2019, by the International Journal of Cancer. Read the abstract of “Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women.”
Hair dye and chemical straighteners
Many people use hair dye. Studies estimate that more than 33% of women older than 18 color their hair. Among black women, using some type of chemical hair straightener is also very common. Research suggests that nearly 75% of black women use some type of chemical relaxer/straightener on their hair.
Research also shows that hair products contain more than 5,000 chemicals, including some considered to be hormone disrupters. Hormone disruptors can affect how estrogen and other hormones act in the body, by blocking them or mimicking them, which throws off the body's hormonal balance. Because estrogen can make hormone-receptor-positive breast cancer develop and grow, many women choose to limit their exposure to these chemicals that can act like estrogen. Other chemicals that make up hair dye have been found to cause mammary gland tumors in rats.
Chemical treatments used to permanently or semi-permanently straighten or relax hair also contain a mixture of chemicals. Many straighteners contain formaldehyde, which is considered a carcinogen, a substance capable of causing cancer.
Past research on any links between hair dye and breast cancer has offered mixed results. A few studies found a link, but many found no association. So the researchers who did this study wanted to add more information to the topic.
About the Sister Study
These results on hair dye and hair straighteners are part of a larger study, called the Sister Study. The Sister Study is an ongoing study by scientists at the U.S. National Institute of Environmental Health Sciences (NIEHS) that includes 50,884 women living in the United States and Puerto Rico. The women joined the study between 2003 and 2009. The women were between the ages of 35 and 74 when they joined the study and none of the women had been diagnosed with breast cancer, but all had at least one sister who had been diagnosed. The Sister Study is looking at the causes of breast cancer and other health issues in women, as well as factors that influence quality of life and outcomes after a breast cancer diagnosis.
When they joined the study, the women answered questions about their health, environment, and lifestyles. The women complete health updates every year and answer detailed questionnaires about their health and experiences every 2 to 3 years.
To look for links between hair dyes and hair straighteners and breast cancer, the researchers sent a questionnaire to the women asking:
- how often they used permanent, semi-permanent, or temporary hair dye or a chemical hair straightener in the 12 months before they joined the study
- how often any type of hair dye or hair straightener was applied at home
- whether the dye used was a dark color or a light color or both
Overall, 46,709 women completed the questionnaire and were included in this analysis.
After 8 years of follow-up, the researchers found:
- Overall, women who regularly used permanent hair dye in the 12 months before joining the study were 9% more likely to develop breast cancer than women who didn’t use hair dye.
- Black women who used permanent hair dye every 5 to 8 weeks or more in the 12 months before joining the study were 60% more likely to develop breast cancer than women who didn’t use hair dye.
- White women who used permanent hair dye every 5 to 8 weeks or more in the 12 months before joining the study were 8% more likely to develop breast cancer than women who didn’t use hair dye.
- There was little increase in breast cancer risk among women who used semi-permanent or temporary hair dye.
- Women who used chemical hair straighteners every 5 to 8 weeks in the 12 months before joining the study were about 30% more likely to develop breast cancer than women who didn’t use chemical hair straighteners.
- The association between using chemical hair straighteners and higher breast cancer risk was similar among black women and white women, but black women were much more likely to use hair straighteners than white women.
“Researchers have been studying the possible link between hair dye and cancer for a long time, but results have been inconsistent,” said corresponding author Alexandra White, head of the NIEHS Environment and Cancer Epidemiology Group. “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.”
Co-author Dale Sandler, chief of the NIEHS Epidemiology Branch, cautioned that although there is some prior evidence to support the association with chemical straighteners, these results need to be replicated in other studies.
When asked if women should stop dyeing or straightening their hair, Sandler said, “We are exposed to many things that could potentially contribute to breast cancer, and it is unlikely that any single factor explains a woman's risk. While it is too early to make a firm recommendation, avoiding these chemicals might be one more thing women can do to reduce their risk of breast cancer.”
What this means for you
It’s important to know that this study found an association between permanent hair dye and chemical hair straighteners and breast cancer; it is not a direct cause-and-effect relationship. In other words, using permanent hair dye and chemical straighteners may increase a woman’s risk of breast cancer, but using these products does not directly cause breast cancer.
“Obviously this topic is useful to look at,” said Larry Norton, M.D., medical oncologist and medical director, Evelyn H. Lauder Breast Center at Memorial Sloan Kettering Cancer Center in New York and member of the Breastcancer.org Professional Advisory Board, in an interview with Forbes. “Does this work merit further study? Yes, absolutely. Does this prove hair straighteners and hair dyes cause breast cancer? No. There’s a weak association but this association does not equal causation,” he added.
It’s also important to know that the women in the study already had a higher than average risk of breast cancer because they had at least one first-degree relative who had been diagnosed with breast cancer.
“What goes in, on, and around us affects how our cells are built and run,” explained Breastcancer.org Founder and Chief Medical Officer Marisa Weiss, M.D. “This includes any food, household, personal care, or other products that we use repeatedly over a long stretch of time.
“Our bodies absorb some of the chemicals in hair dye, hair straighteners, and other hair products, and this article suggests that they may potentially increase the risk of breast cancer in women with a family history of this disease,” she continued. “The most practical and wise approach is to use what's helpful and harmless and to minimize using anything known to be harmful. Dying and straightening your hair helps many people feel better about their appearance, but may be somewhat harmful for your cells. The concern is particularly worrisome for black women. Besides going gray and curly, in-between reasonable steps could include less frequent dying and the use of hormone-free, fragrance-free, less harsh, organic dye and straightening agents.”
Written by: Jamie DePolo, senior editor
Reviewed by: Brian Wojciechowski, M.D., medical adviser