Individuals who reported using chemical hair-straightening products may be at greater risk for uterine cancer compared to those who did not report using these products, according to a new study published by Chang et al in the Journal of the National Cancer Institute (JNCI). The researchers found no associations with uterine cancer for other hair products that the study participants reported using, including hair dyes, bleach, highlights, or perms.

The study, which used data from the National Institute of Environmental Health Sciences’ Sister Study, included 33,497 U.S. patients aged 35 to 74 years, and sought to identify risk factors for breast cancer and other health conditions. The participants were observed for almost 11 years, and during that time, 378 uterine cancer cases were diagnosed. 

Uterine cancer accounts for about 3% of all new cancer cases but is the most common type of cancer of the female reproductive system, with 65,950 estimated new cases in 2022. Studies have shown that incidence rates of uterine cancer have been rising in the United States, particularly among Black patients.

Study Findings

The researchers found that participants who reported frequent use (more than four times in the previous year) of hair-straightening products were more than twice as likely to go on to develop uterine cancer compared to those who did not use the products.

“We estimated that 1.64% of [individuals] 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%,” said lead study author Alexandra White, PhD, MSPH, the Head of the Environment and Cancer Epidemiology group at the National Institute of Environmental Health Sciences. “This doubling rate is concerning. However, it is important to put this information into context—uterine cancer is a relatively rare type of cancer.”

According to the study, approximately 60% of the participants who reported using straighteners in the previous year self-identified as Black women. Although the study did not find that the relationship between hair straightener use and uterine cancer incidence was different by race, the adverse health effects may be greater for Black individuals as a result of higher prevalence of use.

“Because [the study showed that] Black [individuals] use hair straightening or relaxer products more frequently and tend to initiate use at earlier ages than other races, these findings may be even more relevant for [Black individuals],” said study author Che-Jung Chang, PhD, a research fellow in the Epidemiology Branch of the National Institute of Environmental Health Sciences.

The findings were consistent with prior studies showing that straighteners could increase the risk of hormone-related cancers.

The researchers did not collect information on the brands or ingredients in the hair products the participants used. However, they noted that several chemicals that have been found in hair straighteners (such as parabens, bisphenol A, metals, and formaldehyde) could be contributing to the increased risk of uterine cancer. Chemical exposure from hair product use, especially hair straighteners, could be more concerning than other personal care products because of the higher rate of absorption through the scalp—which may be exacerbated by burns and lesions caused by the hair straighteners.

“To our knowledge, this is the first epidemiologic study that examined the relationship between straightener use and uterine cancer,” said Dr. White. “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 [individuals].”

Disclosure: For full disclosures of the study authors, visit academic.oup.com.