The study, published online Dec. 4 in the International Journal of Cancer, concluded breast cancer risk increased with more frequent use of these chemical hair products.
The research team, with the National Institute of Environmental Health Sciences, part of NIH, used data from 46,709 women in the Sister Study and found that women who regularly used permanent hair dye in the year before the study were 9% more likely than women who didn't use hair dye to develop breast cancer.
The increased risk was greater for African American women. Using permanent dyes every five to eight weeks or more was associated with a 60% increased risk of breast cancer, as compared with an 8% increased risk for white women. The research team found little to no increase in breast cancer risk for semi-permanent or temporary dye use.
"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."
The scientists also found a link between chemical hair straighteners and breast cancer. Black and white women who used the straighteners every five to eight weeks were about 30% more likely to develop breast cancer. Although the risk was the same, the study pointed out, African American women are more likely to use chemical straighteners.
“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,” said Dale Sandler, chief of the NIEHS Epidemiology Branch and co-author of the study. “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.”