Frequent chemical hair straightening linked to higher uterine cancer risk, NIH study finds

FILE - The hair-washing sinks at a salon in West Reading, Pennsylvania, on June 22, 2021. (Photo by Ben Hasty/MediaNews Group/Reading Eagle via Getty Images)

Women who use chemical hair straightening products were found to have a higher risk of developing uterine cancer, compared to women who don’t use them, according to a new study from the National Institutes of Health.

The study, which included data from nearly 33,500 U.S. women between the ages of 35 and 74, found no such link for other hair products, including hair dyes, bleach, highlights, or perms. But those who reported using hair straightening products more than four times in the previous year were found to be more than twice as likely to go on to develop uterine cancer, the study found.

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Roughly 60% of the participants who reported using straighteners in the previous year were self-identified Black women, leading the researchers to highlight how such health effects may be greater for this population due to the higher prevalence of use.

"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 Che-Jung Chang, Ph.D., a study and research fellow in the National Institute of Environmental Health Sciences Epidemiology Branch.

Uterine cancer is rare, accounting for about 3% of all new cancer cases in the U.S., but it’s the most common cancer of the female reproductive system, the NIH said. An estimated 65,950 new cases have been reported in 2022.

Studies have also shown that incidence rates of uterine cancer have been rising nationwide, particularly among Black women, the agency noted.

While still rare, ‘doubling rate is concerning,’ study author says

The study data included 33,497 U.S. women participating in the Sister Study, research led by the National Institute of Environmental Health Sciences (NIEHS), part of NIH, that seeks to identify risk factors for breast cancer and other health conditions. 

The women were followed for nearly 11 years, and during that time, 378 uterine cancer cases were diagnosed.

"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%," lead study author Alexandra White, Ph.D., head of the NIEHS Environment and Cancer Epidemiology group, said in a statement. 

"This doubling rate is concerning. However, it is important to put this information into context - uterine cancer is a relatively rare type of cancer," White added.

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The study authors did not collect information on brands or ingredients in the hair straightening products women used. However, they noted that several chemicals commonly found in straighteners — such as parabens, bisphenol A, metals, and formaldehyde — could be contributing to the increased uterine cancer risk.

The researchers said hair straightening products, which can cause burns and lesions during the process, may also lead to increased absorption through the scalp, leading to more chemical exposure.

Prior studies have shown straighteners can increase the risk of hormone-related cancers in women, but this was the first to analyze the relationship between straightener use and uterine cancer, the team said.

"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," White said.

The study team previously published research that suggests women who use permanent hair dye and chemical hair straighteners may have a higher risk of developing breast cancer.

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This story was reported from Cincinnati.