A government study involving nearly 50,000 US women has found a link between those who use permanent hair dyes and chemical straighteners and an increased risk of breast cancer, Fox News reports. Research by scientists with the National Institutes of Health, published in the International Journal of Cancer, involved data from 46,000-plus women between the ages of 35 and 74 who each had had a sister with breast cancer, although they themselves were cancer-free—part of the aptly named "Sister Study." Per a press release, women who regularly used permanent hair dye in the year before they signed up for the study were 9% more likely to get breast cancer than women who kept their tresses natural. For African American women, however, that risk of breast cancer following regular hair dye use was 45%; white women only saw a 7% increase, per Newsweek.
The disparity increased more with heavy dye use, considered once or more every five to eight weeks: Black women had an increased risk of 60%, while white women saw a small increase, to 8%. Women overall who used chemical hair straighteners every five to eight weeks saw a 30% jump in their risk. There was little to no increased risk for women who used semi-permanent or temporary hair dyes. "The results do not surprise me," an oncologist not involved with the study tells Newsweek. Still, experts call for more research. "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," study co-author Dale Sandler says in the release. "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." (Read more discoveries stories.)