Hair-straightening products may significantly increase the risk of developing uterine cancer among those who use them frequently, a large study published on Monday suggests.

“We estimated that 1.64% of women who never used hair straighteners would go on to develop uterine cancer by the age of 70, but for frequent users, that risk goes up to 4.05%,” study leader Alexandra White of the U.S. National Institute of Environmental Health Safety (NIEHS) said in a statement.

“However, it is important to put this information into context. Uterine cancer is a relatively rare type of cancer,” she added.

Still, uterine cancer is the most common gynaecologic cancer in the United States, according to the US Centre for Disease Control and Prevention (CDC), with rates rising, particularly among Black women.

Researchers tracked 33,947 racially diverse women, ages 35 to 74, for an average of nearly 11 years. During that time, 378 women developed uterine cancer.

After accounting for participants’ other risk factors, the odds of developing uterine cancer were more than two and a half times higher for women who had used straightening products more than four times in the previous year.

Less frequent straightener use in the past year also was associated with an elevated uterine cancer risk, but the difference was not statistically significant, meaning it might have been due to chance.

Earlier studies have shown that hair straighteners contain so-called endocrine disrupting chemicals. The products have previously been associated with higher risks of breast and ovarian cancer.

“These findings are the first epidemiologic evidence of association between use of straightening products and uterine cancer,” White and colleagues wrote in The Journal of the National Cancer Institute. “More research is warranted to ... identify specific chemicals driving this observed association.”

The link between straightener use and uterine cancer did not differ by race in the study.

But “because Black women use hair straightening or relaxer products more frequently and tend to initiate use at earlier ages than other races and ethnicities, these findings may be even more relevant for them,” Che-Jung Chang of NIEHS said in a statement.

AE News