En español | Permanent hair dyes and chemical hair straighteners may be associated with an increased risk of breast cancer, especially for black women, according to a study published Dec. 4 in the International Journal of Cancer.
Researchers at the National Institute of Environmental Health Sciences, part of the National Institutes of Health (NIH), followed 46,709 cancer-free women ages 35 through 74 for an average of 8.3 years, during which time 2,794 of them developed breast cancer.
Black women who regularly used permanent dyes (meaning every five to eight weeks or more) in the year prior to enrolling in the study had a 60 percent increase in breast cancer risk compared to those who didn't use permanent dyes. Among white women who regularly used permanent dyes, there was an 8 percent increase.
Breast cancer risk was also 31 percent higher for women who regularly used chemical straighteners, regardless of race. But the study authors say that association might be more important for black women, 74 percent of whom reported using chemical straighteners in the year prior to the study, compared to 3 percent of white women.
Black women and breast cancer risk
According to the Centers for Disease Control and Prevention, black women die of breast cancer more often than white women, even though the two groups get breast cancer at about the same rate. Black women are less likely to be diagnosed with the disease in its early stages, and are more likely to be diagnosed with triple-negative breast cancer, an aggressive form of the disease that often recurs after treatment.
Researchers have long known that dyes and chemical straighteners can include potentially cancer-causing and hormone-disrupting compounds, which may affect breast cancer risk. The carcinogen formaldehyde, for example, is an active ingredient in many keratin hair straightening treatments.
Hair products marketed toward black women have also been found to contain higher levels of hormone-disrupting chemicals. The study authors note that differences in hair texture may also influence how much dye women use during the application process, and how much is needed or absorbed.
More research is needed, they say, to identify specific ingredients that affect disease risk and to better examine the link between product use and breast cancer risk by racial group. Only about 9 percent of study participants in this case were black women, and other racial groups, like Hispanic and Asian women, were not included in their analysis.
In a list of frequently asked questions about their findings, the authors write that chemical hair products are, ultimately, “just one of many factors” that influence breast cancer risk. They suggest that permanent dye users consider switching to semi-permanent or temporary dyes, which were not associated with an increased cancer risk, and to take proper precautions while applying dye, like wearing gloves and rinsing the product out according to instructions.