Chemically straightening and relaxing hair has been commonplace for women – especially Black women – for decades, but a new study published by the National Institutes of Health indicates that there could be a link between chemically straightening hair and uterine cancer. 

The 11-year-long study, which was carried out in the US, surveyed nearly 34,000 women between the ages of 35 and 74 who came from diverse racial and ethnic backgrounds. It showed that the women who used chemical straightening products frequently (more than four times in the previous year) were more than two times as likely to develop uterine cancer by age 70 than those who did not. Although Black women made up a minority of the study participants (just 7.4%), they were the demographic that was most largely affected – with 60% of that group reporting to use hair straightening products.

Uterine cancer (also known as womb or endometrial cancer) is the fourth most common cancer in women in the UK and the most common of the five gynaecological cancers, with around 9,700 new cases every year. The researchers found no associations with uterine cancer for other hair products that the women reported using, including hair dyes, bleach, highlights or perms.

“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 percent,” said Alexandra White, PhD, head of the National Institute of Environmental Health Sciences environment and cancer epidemiology group and lead author on the 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.”

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

While the study is alarming, Crystal Aguh, MD, hair expert and associate professor of dermatology at Johns Hopkins School of Medicine, also points out that there’s more context to the study to keep in mind. “This study, called the Sister Study, conducts surveys on participants who have at least one sister who has been diagnosed with breast cancer, so presumably this population has a higher risk of developing breast (or other gynaecologic cancers) than most women,” she explained in a tweet. 

So is there cause for concern and should we think about limiting our use of chemical straighteners? “There are many factors that may cause uterine cancer,” Mr Saurabh Phadnis, consultant gynaecologist and gynaecological oncologist at London Gynaecology tells Stylist. “Although this study has shown a link between use of straightening chemicals and cancer it does not prove a direct cause-effect relation. Therefore, we cannot advise to discontinue this practice.”

More information and advice on gynaecological cancers can be found at The Eve Appeal, the UK’s leading charity funding research and raising awareness into the five gynaecological cancers – womb, ovarian, cervical, vulval and vaginal.

Main image: Getty