Hair straightening chemicals linked to increased risk of uterine cancer

TRIANGLE PARK, N.C. — Women who use chemicals to straighten their hair may be doubling their risk for a rare form of cancer. Researchers with the National Institute of Environmental Health Sciences (NIEHS) say they have found a link between these hair chemicals and higher rates of uterine cancer among women.

The team notes that their findings do not show the same risk among other hair products, such as hair dye, bleach, highlights, or perms.

The results come from an analysis of 33,497 women throughout the United States who were taking part in the Sister Study. All of these participants were between the ages of 35 and 47 and scientists kept track of their health for roughly 11 years. During that time, there were 378 cases of uterine cancer.

The team found that women who reported using hair straightening chemicals frequently (at least four times per year) saw their cancer risk more than double compared to women who did not use those chemicals.

“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%,” says lead author Alexandra White, Ph.D., head of the NIEHS Environment and Cancer Epidemiology group, in a media release. “This doubling rate is concerning. However, it is important to put this information into context – uterine cancer is a relatively rare type of cancer.”

What is uterine cancer?

Uterine cancer makes up roughly three percent of all new cancer diagnoses. However, it is also the most common cancer of the female reproductive system. Researchers say there were approximately 65,950 new cases in 2022. Cases of the disease have been rising in the U.S. — especially among Black women.

With that in mind, study authors note that 60 percent of the participants who reported using hair straightening chemicals were Black. Although the study did not find a significant difference in the risk of cancer based on race, researchers say people who use more face more danger.

“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,” adds study author Che-Jung Chang, Ph.D., a research fellow in the NIEHS Epidemiology Branch.

What’s is hair straightening chemicals that could make it toxic?

Study authors say these products may contain parabens, bisphenol A, metals, and formaldehyde. Any or all of these chemicals could be contributing to higher rates of cancer onset, the team says. They believe that the chemicals may absorb into the body through the scalp.

“To our knowledge this is the first epidemiologic study that examined the relationship between straightener use and uterine cancer,” White concludes. “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.”

The findings are published in the Journal of the National Cancer Institute.

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