The use of chemical hair straightening products is associated with an increased risk of uterine cancer, according to research published in the Journal of the National Cancer Institute.

Researchers observed an 80% higher risk of uterine cancer among study participants who had used straightening products, and that risk increased with more frequent use.

“Previous studies have found hair product use to be associated with a higher risk of hormone-sensitive cancers, including breast and ovarian cancer; however, to our knowledge, no previous study has investigated the relationship with uterine cancer,” the researchers wrote.

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The team tested for associations between hair product use and uterine cancer among participants in the Sister Study ( Identifier: NCT00047970). That study enrolled a large group of women who had no history of breast cancer but had at least 1 sister with breast cancer.

The current analysis included 33,947 Sister Study participants who were 35-74 years of age and had a uterus when they were enrolled between 2003 and 2009. The participants had a mean age of 54.2 years at baseline. Most participants (85.6%) were non-Hispanic White, 7.4% were Black/African American, 4.4% were non-Black Hispanic/Latina, and 2.5% belonged to other racial/ethnic groups.

The participants self-reported use of hair products in the prior 12 months. The products included hair dyes (permanent, semipermanent, and temporary), straighteners (chemical straightener, relaxer, and pressing products), and hair permanents or body waves.

At a mean follow-up of 10.9 years, there were 378 cases of uterine cancer. In an adjusted analysis, there was an 80% higher risk of uterine cancer among participants who had used straighteners in the 12 months prior to baseline (hazard ratio [HR], 1.80; 95% CI, 1.12-2.88). The association was stronger when comparing frequent use (>4 times in the 12 months prior to baseline) with no use of straightening products (HR, 2.55; 95% CI, 1.46-4.45; Ptrend =.002).

Among participants who had not used straighteners, 1.64% were predicted to develop uterine cancer by age 70. The estimated risk was 1.18% higher for participants who had used straighteners in the 12 months prior to baseline and 2.41% higher for those with frequent straightener use in the 12-month period (>4 times).

The researchers did not find any associations between the use of other hair products and uterine cancer.

The researchers noted that several chemicals found in hair straightening products — parabens, bisphenol A, cyclosiloxanes, diethanolamine, metals, and formaldehyde — could contribute to the increased risk in uterine cancer observed in this study.

In addition, higher percutaneous absorption of chemicals has been observed in the scalp compared with other skin. And heating processes used during straightening treatments could release or thermally decompose chemicals from the products, leading to potential higher exposures to hazardous chemicals.

“Given the widespread use of hair products and the rising incidence of uterine cancer, our findings, which identify hair straightener use as a potential target for intervention, are particularly relevant for public health approaches to reduce uterine cancer incidence,” the researchers concluded.

Limitations of this study include self-reported product use, potential variation in product use over time, and no collection of information on brands or ingredients of hair products.


Chang C-J, O’Brien KM, Keil AP, et al. Use of straighteners and other hair products and incident uterine cancer. J Natl Cancer Inst. Published October 17, 2022. doi:10.1093/jnci/djac165