Uterine cancer: Chemical hair straighteners double risk

• Uterine cancer is the sixth most commonly diagnosed cancer in women around the world.
• A new study from the National Institutes of Health has found that women who use hair straightening products are twice as likely to develop uterine cancer than those who do not.
• Researchers believe Black women may be at increased risk due to a higher usage rate of hair straightening products.

Uterine cancer, also called endometrial cancer, is the sixth most commonly occurring cancer for women around the world, with more than 417,000 cases reported in 2020.

Research shows the rate of endometrial cancer increased globally from 1990 to 2019.

Now a new study from the National Institutes of Health (NIH) says that women who frequently use hair straightening products are twice as likely to develop uterine cancer compared to women who do not use them.

Researchers also found Black women may be at an increased risk due to a higher usage rate of hair straightening products.

This study recently appeared in the Journal of the National Cancer Institute.

What is uterine cancer? 

Uterine cancer occurs in the uterus — a female organ involved in reproduction. The uterus is also called a womb.

The most common type of uterine cancer, known as endometrial cancer, happens in the inner lining of the uterus, called the endometrium. Uterine cancer can also take place in the muscle wall of the uterus called the myometrium.

Risk factors for uterine cancer include:

• age
• obesity
• family history
• type 2 diabetes
• exposure to or imbalance of estrogen.

Symptoms of uterine cancer include:

• unusual bleeding between menstrual cycles or after menopause
• pelvic pain
• pain during urination
• fatigue
• nausea
• a feeling of heaviness in the pelvic area
• weight loss.

Hair products and cancer risk

According to Dr. Alexandra White, head of the National Institute of Environmental Health Sciences (NIEHS) Environment and Cancer Epidemiology group — a part of the NIH — and lead author of this study, hair products such as dye and chemical straighteners contain a number of different chemicals that may act as carcinogens or endocrine disruptors, and thus may be important for cancer risk.

“Straighteners in particular have been found to include chemicals such as phthalates, parabens, cyclosiloxanes, [and] metals, and can release formaldehyde when heated,” she told Medical News Today.

“Previous research has suggested that hair dye and chemical straighteners are related to other hormone-sensitive cancers, such as breast and ovarian cancer, but no previous study has considered how they are related to uterine cancer risk,” said Dr. White.

For this study, Dr. White and her team studied data from over 33,000 women in the United States aged 35–74 years participating in the Sister Study. The NIEHS conducts the Sister Study in an effort to identify breast cancer risk factors and other health issues.

Researchers followed women participating in the study for about 11 years. During that time, 378 cases of uterine cancer were diagnosed.

Upon analysis, the scientists found that women who said they used hair straightening products more than four times in 1 year were more than twice as likely to develop uterine cancer than those who did not use the products.

“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%,” Dr. White says.

Researchers reported not finding any increased risk for uterine cancer for women using other hair care products such as hair dyes, highlighting products, bleach, or perming products.

Increased risk for Black women

According to researchers, 60% of participants who used hair straightening products self-identified as Black women. Although scientists did not find a link between chemical hair straightener use, uterine cancer diagnosis, and race, the research team reported Black women may be at increased risk due to higher use of chemical hair straighteners.

“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,” states Dr. Che-Jung Chang, a research fellow in the NIEHS Epidemiology Branch and member of the study’s research team.

A study from June 2022 found that incidents of uterine cancer were on the rise among non-Hispanic Black women. This same study also found that Black women had more than double the mortality rate compared to other racial and ethnic groups.

More evaluation needed

When asked about the next steps for this research, Dr. White said they are now evaluating other personal care product use mixtures in relation to cancer risk and considering how the use of hair straighteners across the life course may influence cancer risk.

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

“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,” she cautions.

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