Published in medical journal Carcinogenesis, the study looked at more than 4000 women from New York and New Jersey, aged between 20 and 75, 2280 of whom have had breast cancer.
Researchers asked the women if they had ever used permanent hair dye at least twice a year over the course of at least one year, Reuters reports. They were also asked if they had ever used chemical hair relaxants or straighteners for at least one year.
The concerning research found that white women who used chemical straighteners had a 74 per cent increased risk of breast cancer, while black women who used dark hair dye had a 51 per cent increased risk.
Women who both had their hair dyed dark and chemically straightened regularly had an even higher breast cancer risk, news.com.au reports.
“These novel findings support a relationship between the use of some hair products and breast cancer,” the study concludes. “Further examinations of hair products as important exposures contributing to breast cancer carcinogenesis are necessary.”
Lead author Adana Llanos, epidemiologist at Rutgers School of Public Health, New Jersey, says the findings are concerning but not definitive.
“Our findings do not suggest that simply using hair dyes, relaxers or both will cause a woman to get breast cancer,” she told the Chicago Tribune. “What I think is really important is we need to be more aware of the types of exposures in the products we use.”
Cancer Council Australia notes that occupational exposure to hair dyes was classified as a probable carcinogen by the International Agency On Cancer Research in 2009, but says personal use was not classified as carcinogenic at this stage.