The study tracked 33,497 women in the United States between the ages of 35 and 74 as they used hair dyes, straighteners, relaxers or pressing products for, on average, over a decade. About 60 percent of the participants self-identified as Black women in the study, which was published in the peer-reviewed Journal of the National Cancer Institute on Monday — with 378 uterine cancer cases diagnosed over that time.

It found that women who reported frequent use of hair-straightening products were more than twice as likely to develop uterine cancer compared with those who did not use the products.

“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 author Alexandra White, from the National Institute of Environmental Health Sciences, 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.”

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“Hair products may contain hazardous chemicals with endocrine-disrupting and carcinogenic properties,” the report said. “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.”

Che-Jung Chang, a study author and research fellow, noted that the findings are especially relevant for Black women because they “use hair straightening or relaxer products more frequently and tend to initiate use at earlier ages than other races and ethnicities.”

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Despite a growing natural-hair movement, many Black people in the United States and elsewhere have faced discrimination at school and work for wearing their hair that way, with some saying they receive better treatment when they straighten. And damage caused by heat and chemical straightening has long been a concern for Black women.

In March, the House passed the Crown Act (Creating a Respectful and Open World for Natural Hair), legislation that would ban discrimination against people based on how they wear their hair.

The study found no associations with uterine cancer for other hair products that the women reported using, such as dyes, bleach, highlights or perms. The same team found in a 2019 study that permanent hair dye and straighteners may, however, increase breast- and ovarian-cancer risk.

Uterine cancer accounts for just over 3 percent of all new cancer cases in the United States, according to the U.S. National Cancer Institute, with recent studies showing incidence rates on the rise in the country, particularly among Black women.

Cancer of the uterus is the most common gynecologic cancer in the United States, according to the Centers for Disease Control and Prevention. In 2019, the latest year for which data is available, 59,450 new cases of uterine cancer were reported among U.S. women, and 11,556 died of it.

Its symptoms can include vaginal discharge or bleeding that is abnormal to the individual and pain in the pelvis, and it is generally more common in women who have gone through menopause. Factors that increase risk include obesity, genetics and being over 50, according to the CDC, and treatment can involve surgery, chemotherapy or radiation.

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The study did not identify specific brands or ingredients used by the participants but noted that several chemicals in straighteners may contribute to the increased risk, such as parabens, bisphenol A, metals and formaldehyde. It called for more research “to identify specific chemicals driving this observed association.”

The method of application is also a factor, it added, given that most products are applied for long periods, leading to 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,” added White, the lead author.