NIH Record - National Institutes of Health

Study Finds Hair-Straightening Chemicals Raised Uterine Cancer Risk

Women who used chemical hair-straightening products were at higher risk for uterine cancer compared to women who did not report using these products, according to a new NIH study. The researchers found no associations with uterine cancer for other hair products that the women reported using, including hair dyes, bleach, highlights or perms.

The study data includes 33,497 U.S. women ages 35-74 participating in the NIEHS-led Sister Study that seeks to identify risk factors for breast cancer and other health conditions. The women were followed for almost 11 years. During that time 378 uterine cancer cases were diagnosed. 

The researchers found that women who reported frequent use of hair-straightening products, defined as more than four times in the previous year, were more than twice as likely to develop uterine cancer.

Dr. Alexandra White
Dr. Alexandra White

“We estimated that 1.64 percent 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 percent,” said Dr. Alexandra White, head of the NIEHS environment and cancer epidemiology group and lead author on the new study. “This doubling rate is concerning. However, it is important to put this information into context; uterine cancer is a relatively rare type of cancer.”

Uterine cancer accounts for about 3 percent of all new cancer cases but is the most common cancer of the female reproductive system, with 65,950 estimated new cases in 2022. 

Studies show that incidence rates of uterine cancer have been rising in the U.S., particularly among Black women.

Approximately 60 percent of participants who reported using straighteners in the previous year were self-identified Black women, according to the study published in the Journal of the National Cancer Institute

“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,” said Dr. Che-Jung Chang, a study author and research fellow in the NIEHS Epidemiology Branch.

Dr. Che-Jung Chang
Dr. Che-Jung Chang

The researchers did not collect information on brands or ingredients in the hair products the women used. However, in the paper they note that several chemicals found in straighteners (such as parabens, bisphenol A, metals and formaldehyde) could be contributing to the increased uterine cancer risk observed. 

Chemical exposure from hair product use, especially straighteners, could be more concerning than other personal care products due to increased absorption through the scalp, which may be exacerbated by burns and lesions caused by straighteners.

“More research is needed to confirm these findings in different populations to determine if hair products contribute to health disparities in uterine cancer and to identify the specific chemicals that may be increasing the risk of cancers in women,” said White. 

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