Plenty of women enjoy a good hair dye or chemical hair straightener, such as a relaxer. But according to new findings by researchers at the National Institute of Environment Health Sciences (NIEHS) and published in the International Journal of Cancer, women who use such products are more likely to develop breast cancer, reports the National Institutes of Health.

Researchers used data from 46,709 women involved in the Sister Study—a study conducted by the NIEHS that sought to find causes of breast cancer by examining women ages 35 to 74 whose sister had the disease. Findings showed that women who regularly used permanent hair dye were 9% more likely than those who didn’t use hair dye to develop breast cancer.

For Black women, permanent dye use every five to eight weeks or more was linked to a 60% greater risk of developing breast cancer, compared with an 8% increased risk for white women. There was little to no increase in breast cancer risk for women who used semipermanent or temporary dye.

Chemical hair straighteners were also linked to increased risk. Using them at least every five to eight weeks was associated with a 30% more likelihood of developing this cancer. While the association was similar in both Black and white women, straightener use is much more common among Black women.

Although these kinds of observational studies don’t prove cause and effect, this statistical association was strong enough that experts suggested women may want to consider avoiding regular use of permanent dyes and 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, PhD, study coauthor and chief of the NIEHS Epidemiology Branch. “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.”

For similar coverage, read about how inky hair dyes may pose a higher risk for cancer in “Fear of the Dark.”