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Chemical Hair Straighteners Are Linked to Uterine Cancer, Scientists Warn: ScienceAlert

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Rare and aggressive uterine cancers are on the rise in the United States, particularly among people of color, and a new study suggests that chemical straighteners may be partly to blame.

For almost 11 years, researchers at the US National Institute of Environmental Health Sciences (NIEHS) followed 33,947 adults who had a uterus after enrolling in the study. During this time, 378 cases of uterine cancer were detected.

Those who used chemical straightening products more than four times in the 12 months prior to participating in the survey were 155 percent more likely to be diagnosed with uterine cancer later on, compared to those who had never received any straightening treatments.

To put it in perspective, those who have never used hair straightening products have a 1.64 percent chance of being diagnosed with uterine cancer by their 70th birthday. That number goes up to 4.05 percent for those who chemically straighten their hair frequently—a still small but significantly higher risk.

Hair dyes, meanwhile, were not linked to uterine cancer.

“These findings are the first epidemiological evidence of an association between the use of straightening products and uterine cancer,” write the researchers at NIEHS.

The worrying results are the latest in a series of recent studies on commonly used chemicals that disrupt the endocrine system; Messenger chemicals that bind the hormones in our body to their target organs.

Excess hormones such as estrogen and progesterone have been linked to uterine cancer in the past, and many hair products can mimic these natural hormones and bind to their receptors.

In 2018, researchers found endocrine-disrupting chemicals in 18 hair products tested. What’s more, 84 percent of the chemicals identified were not listed on product labels, and 11 products contained chemicals prohibited under the European Union Cosmetics Directive or regulated by California law.

Currently, federal regulations in the US require that estrogen receptor activity be tested only in the case of pesticides and drinking water contaminants. Hair products are left out and this can seriously harm public health.

In 2019, an NIH-funded study found that permanent hair dye and straightening chemicals are associated with a higher risk of breast cancer, especially among black women who tend to get these treatments more often.

A follow-up study in 2021 found that permanent hair dye and straightening chemicals were also associated with a higher risk of ovarian cancer.

Now, uterine cancer can be added to the list. The study on this last type of cancer did not identify differences between racial and ethnic groups, but the authors note that the dangers may be greater because Black women use straightening products at younger ages, at higher rates, and in higher concentrations. One study found that 89 percent of African American women reported using chemical relaxers or straighteners.

Researchers at the NIH are still trying to figure out which specific chemicals in hair products might explain the associated carcinogenic effects, but parabens, phthalates, and formaldehyde are some of the leading suspects.

The human scalp also easily absorbs chemicals that cannot pass through thicker areas of skin or those with fewer hair follicles, such as the palms or abdomen. Flat-ironing or blow-drying can also thermally degrade chemicals into the hair, resulting in potentially more dangerous effects.

“We observed stronger associations with straightener use among women with low physical activity,” the authors write.

“As physical activity is associated with decreased sex steroid hormones and less chronic inflammation, women with higher physical activity may be less susceptible to other risk factors for uterine cancer. However, further studies are warranted to understand the relationship between physical activity and hair product. use and uterine cancer.”

About half of all women in the US have used permanent hair dye at some point, and smoothing keratin treatments and Brazilian blowouts are becoming increasingly popular.

Hairdressers and their clients deserve to know what these products do for their health.

The study was published in: Journal of the National Cancer Institute.