Women who regularly use permanent hair dye and chemical hair straighteners may face a higher breast cancer risk, according to the National Institutes of Health.

Data from the more than 46,000 participants in the Sister Study showed the link to be greatest among African American women. Those who used permanent dyes every five to eight weeks or more had a 60% increased risk of breast cancer, compared to an 8% increased risk for white women.

“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,” said the study’s corresponding author, Alexandra White, Ph.D.

Semi-permanent and temporary dyes, on the other hand, were not implicated in increasing risk. But hair straighteners were. All study participants who used these products at least every five to eight weeks were about 30% more likely to develop breast cancer. This was true even though straightener use was more common among African American study participants.

The researchers cautioned that it is unlikely that one risk factor explains a woman’s likelihood of developing cancer, and that the results need to be replicated in future studies. That said, “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,” said study co-author Dale Sandler, Ph.D.

The study was published online Dec. 4 in the International Journal of Cancer