Chemical hair straighteners are linked with an increased risk of uterine cancer, suggests new study

A new study conducted by researchers at the US National Institutes of Health (NIH) suggests that chemical straighteners are associated with an increased risk of uterine cancer, according to an institutional press release.

For 11 years, researchers tracked 33,947 adults with a uterus aged between 35 and 74. During this period, 378 of the subjects were diagnosed with uterine cancer.

The research also demonstrated that those who frequently used hair-straightening chemicals (more than four times last year), were 155 percent more likely to later be diagnosed with uterine cancer when compared to those who never had a hair-straightening treatment.

“We estimated that 1.64 percent 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 percent,” said Alexandra White, Ph.D., head of the NIEHS Environment and Cancer Epidemiology group and lead author on the new study.

“This doubling rate is concerning. However, it is important to put this information into context - uterine cancer is a relatively rare type of cancer.”

Uterine cancer is rare, but is the most common cancer of the female reproductive system

Accounting for about three percent of all new cancer cases, uterine cancer is relatively rare, but is the most common cancer of the female reproductive system.

On the other hand, a previous study funded by the NIH demonstrates that uterine cancer rates are increasing in the United States, especially among Black women. This is significant because chemical hair-straightening treatments are more prevalently preferred by Black women.

“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, Ph.D., an author of the new study and a research fellow in the NIEHS Epidemiology Branch.

Researchers did not work on brands or ingredients found in hair products specifically, but they also stated in the paper that a number of chemicals in straighteners, such as parabens, bisphenol A, metals, and formaldehyde, could be responsible for the increased uterine cancer risk.

New study aligns with earlier studies

The chemicals from hair products, especially straighteners, may be more worrisome than other personal care products because burns and lesions brought on by straighteners may make increased absorption through the scalp worse.

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

The results are in line with earlier research suggesting that the use of hair straighteners may raise the risk of hormone-related cancers such as breast and ovarian cancer.

The results of the study were published in the Journal of the National Cancer Institute.

Abstract:

Background: Hair products may contain hazardous chemicals with endocrine-disrupting and carcinogenic properties. 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.

Methods: We examined associations between hair product use and incident uterine cancer among 33 947 Sister Study participants aged 35-74 years who had a uterus at enrollment (2003-2009). In baseline questionnaires, participants in this large, racially, and ethnically diverse prospective cohort self-reported their use of hair products in the prior 12 months, including hair dyes; straighteners, relaxers, or pressing products; and permanents or body waves. We estimated adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) to quantify associations between hair product use and uterine cancer using Cox proportional hazard models. All statistical tests were 2-sided.

Results: Over an average of 10.9 years of follow-up, 378 uterine cancer cases were identified. Ever vs never use of straightening products in the previous 12 months was associated with higher incident uterine cancer rates (HR = 1.80, 95% CI = 1.12 to 2.88). The association was stronger when comparing frequent use (>4 times in the past 12 months) vs never use (HR = 2.55, 95% CI = 1.46 to 4.45; Ptrend = .002). Use of other hair products, including dyes and permanents or body waves, was not associated with incident uterine cancer.

Conclusion: These findings are the first epidemiologic evidence of association between use of straightening products and uterine cancer. More research is warranted to replicate our findings in other settings and to identify specific chemicals driving this observed association.