Chemical hair straightening products may increase risk of gynaecological cancers

Several studies published recently reported that the use of chemical hair products may be associated with a higher risk of hormone-related cancers including ovarian and endometrial cancers.

The most recent study was published in the prestigious Journal of the National Cancer Institute. The authors examined associations between hair product use and the incidence of uterine cancer among 33,947 study participants aged 35-74 years who had a uterus at enrolment.  

In questionnaires at the start of the study, participants answered questions on their use of hair products in the prior 12 months. The products included hair dyes (permanent, semipermanent, and temporary), straighteners (chemical straightener, relaxer, and pressing products), and hair permanents or body waves.

Over an average of almost 11 years of follow-up, 378 uterine cancer cases developed. Women who had reported using chemical hair straightening products were more than twice as likely to have developed uterine cancer than those who did not.

Woman with Red Curly Hair

Researchers observed an 80% higher risk of uterine cancer among study participants who had used chemical straightening products, and that risk increased with more frequent use (more than 4 times in the past 12 months)

They estimated that 1.64% of women who never used chemical hair straighteners would go on to develop uterine cancer by the age of 70; but for frequent users of chemical hair straighteners that risk goes up to 4.05%.

The study did not find links between uterine cancer and the use of other hair products, including hair dyes, highlights, and perms.

I can see two possible explanations for this strong risk association:

• There is a possibility that a specific chemical is driving this association between chemical hair straighteners and uterine cancer risk (such as parabens, bisphenol A, metals, and formaldehyde).  Earlier studies have shown that chemical hair straighteners contain endocrine-disrupting chemicals. Chemicals used in hair products might be absorbed through the scalp. Higher absorption of chemicals has been observed in the scalp compared with skin on other areas of the body. When the heating processes occur during straightening treatments, this could potentially increase the release of these chemicals from the products, leading to potential higher exposures of the chemicals.

• The other possibility is that certain genes that give women curly hair, may also cause an increased risk of breast, ovarian and endometrial cancers.

It’s important to note, while the researchers found a possible link between chemical hair straightener use and uterine cancer, they did not conclude from this study that using these products directly causes uterine cancer.

The researchers also note some limitations of the study. The study asked participants to remember product use over the last 12 months, which can be subject to an individual’s ability to remember exact product usage. Chemicals in products may also change over time (participants were enrolled between 2003 and 2009) leading to a potential variation in products used which are available today. The researchers also did not collect information on brands or ingredients of hair products.

Until we know more, I would discourage girls and women from using chemical hair straighteners until research has determined the cause for this association and whether any specific chemicals are driving this association.

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