A new study published in the Journal of the National Cancer Institute has linked the rise of rare and aggressive uterine cancers, particularly in black women, partly to hair straightener chemicals. The study of 33,947 adult women, conducted over nearly 11 years, observed 378 cases of uterine cancer. Women who had used hair straightening chemicals in the last 12 months were up to 4 times more likely to develop uterine cancer than women who had never used hair straightening chemicals. To put this into perspective, the risk increases from 1.64% in women who never use hair straighteners to 4.05% in women who use hair straighteners daily. While this risk may seem small, it is a significant increase. There was also no association between hair dyes and uterine cancer. “These findings are the first epidemiologic evidences of an connection between the use of straightening products and uterine cancer,” say researchers at NIEHS. These worrying results are because the chemicals used disrupt the endocrine (hormone) system. Normally, messenger chemicals link hormones to target organs. Previously, excess estrogen and progesterone hormones have been linked to uterine cancer. The chemicals in most hair products mimic these hormones and bind to receptors, increasing cancer risk. In 2018, researchers have found endocrine-disrupting chemicals in 18 hair products tested.
What’s more, 84 percent of the chemicals not identified on the products’ labels were found in the ingredients. In addition, 11 products contained chemicals banned under the European Union Cosmetics Directive or regulated under California law. Currently in the US, federal law only requires testing for estrogen receptor activity in the case of pesticides and drinking water contaminants. Hair products are excluded, which could cause serious harm to public health. Black Women Start Using Hair Products Earlier In 2019, an NIH-funded study examining chemicals in permanent hair dye and straighteners found that more frequent use was associated with a higher risk of breast cancer, especially in women of color. A follow-up study in 2021 found that chemicals in permanent hair dye and straighteners were also associated with a higher risk of ovarian cancer. Uterine cancer can now be added to this list.
Although the latest study found no difference in race and ethnic groups, it is stated that the risk increases in black women because straightening products start to be used at a younger age and in large quantities. Another study found 89% of African-American women use chemical straighteners and stylers. Researchers at the NIH are still trying to figure out which specific chemicals in hair products could explain the associated carcinogenic effects, but parabens, phthalates, and formaldehyde top the list of suspects. The human scalp also readily absorbs chemicals that cannot pass through thicker areas of skin or those with fewer hair follicles, such as the palms or abdomen. By straightening or blow-drying hair, chemicals in the hair can be thermally degraded, creating more dangerous effects. “We observed a strong association between hair straightener use and low physical activity among women,” the authors write. “Because 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 research may be needed to clarify the association between physical activity and hair product care products and uterine cancer,” the researchers conclude. In the US alone, half of the women have used permanent hair dye, smoothing keratin products, and Brazilian blow-dries at some point in their lives. Of course, hairdressers and customers need to see how healthy hair care products are.