(CNN)Permanent hair dye and chemical hair straightener use was linked to a higher risk of breast cancer in a new study from researchers at the National Institutes of Health. The risk is more than six times higher for black women.
The study, published Wednesday in theInternational Journal of Cancer, followed 46,709 women, all part of the Sister Study, a National Institute of Environmental Health cohort of women whose sisters had been diagnosed with breast cancer. (Family history of breast cancer is considered a risk for developing breast cancer.)
It found that, overall, women who said they used permanent hair dye in the year before enrolling in the study were 9% more likely to develop breast cancer when compared with women who did not.
The risk was substantially higher among black women.
Black women were less likely to use permanent hair dye but significantly more likely to be diagnosed with breast cancer after using it.