A 2022 study, published October 17 in the Journal of the National Cancer Institute, is showing that there’s evidence of association between use of hair-straightening products and uterine cancer, and women who frequently use chemical hair-straightening products could face more than twice the risk of uterine cancer compared to those who never use them.

“More research is warranted to replicate our findings in other settings and to identify specific chemicals driving this observed association,” authors Dr Che-Jung Chang et al wrote.

The study was conducted against the background that hair products may contain hazardous chemicals with endocrine-disrupting and carcinogenic properties. The authors 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, no previous study had investigated the relationship with uterine cancer.

They examined associations between hair product use and incident uterine cancer among 33,947 Sister Study participants. The Sister Study is a prospective cohort that enrolled 50,884 women. Participants were eligible if they were breast cancer-free women aged 35-74 years who had at least one sister diagnosed with breast cancer. 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. The study population consisted of 7.4 per cent black/African American, 4.4 per cent Hispanic/Latina non-black, 85.6 per cent non-Hispanic white, and 2.5 per cent all other race and ethnicity.

Over an average of 10.9 years of follow-up, 378 women developed uterine cancer, which primarily affects tissue lining the uterus called the endometrium. Type 1, the most common form of the cancer, is thought to be linked to having too much of the sex hormone oestrogen.

Women who reported using hair-straightening products in the past year were almost twice as likely to develop uterine cancer compared to women that never used them, the researchers found.

The link was stronger still for frequent users — defined as more than four uses in the past 12 months. These women had around 2.5 times the risk of developing the cancer compared to women who never used the products.

Uterine cancer is one of the most common gynaecologic cancers. Exposure to excess oestrogen and a hormonal imbalance of oestrogen and progesterone have been identified as key risk factors for uterine cancer. Thus, it has been hypothesised that synthetic oestrogenic compounds, such as endocrine-disrupting chemicals (EDCs), could contribute to uterine cancer risk because of their ability to alter hormonal actions.

The authors said that hair product use, a predominant exposure pathway to various EDCs, has been associated with hormone-sensitive cancers, including breast and ovarian cancer in previous epidemiologic studies. Hair product constituents, including formaldehyde and formaldehyde-releasing chemicals in some straighteners, and oxidised para-phenylenediamine and 4-aminobiphenyl in hair dyes have also played a potential role in carcinogenesis, supporting an association between hair product use and cancer development.