A large study found a link between hair straightening products and uterine cancers, especially for Black women

• A decade-long NIH study of 33,000 women found a link between chemical hair straighteners and uterine cancer.
• Black women made up a majority of participants who said they use hair straighteners.

A large government-run study identified a link between hair straightening products and a higher risk for uterine cancer — and the authors said the trend disproportionately affects Black women.

The National Institutes of Health led a study of more than 33,000 women aged 35 to 74 intended to identify risks for breast cancer and other diseases.

After following the women for 11 years, researchers discovered a higher rate of straightener product use among the 378 people who developed uterine cancer.

Frequent users of chemical hair straighteners had a 4% likelihood of developing cancer — nearly double the 1.64% likelihood for women who did not use the products.

Uterine cancer is a rare, hard-to-treat type of cancer that occurs in womb. Deaths from uterine cancer are rising in the US, particularly among Black women, according to a recent analysis by the National Cancer Institute.

The study has caveats. The researchers did not collect information on the brands or chemicals in the hair straightening products, though they suspect formaldehyde, a human carcinogen found in some cosmetics, might account for the heightened cancer risk.

It is also an observational study, and the authors said more research is required to determine whether chemicals in hair products are directly giving people cancer, or if their findings are merely coincidence.

More research into risks of cosmetics marketed to Black women

60% of people who reported using these products self-identified as Black.

"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, a research fellow at NIH and an author on the study.

The research builds on previous studies into whether Black women are at higher risk for possible health hazards linked to hair products. A previous NIH study found an association between breast cancer risk and hair dye use in Black women.

Another study, conducted by researchers at the City of Hope, found parabens, a preservative used in hair products, increased the growth of breast cancer cells in Black women. Researchers analyzed cells in a laboratory and could not determine if the phenomenon would occur in cells living inside the body. Clinical trials, the "gold standard" for medical research, have not established a link between the small amounts of parabens in cosmetics and cancer.