Women who frequently use chemical hair straightening products could be more than twice as likely to develop cervical cancer than those who never use them, according to a new study published Monday.

The findings, published in the Journal of the National Cancer Institute, are particularly relevant to black women, who make up the majority of straightening product users in the United States.

Scientists commended the work and called for action, although more work is needed to confirm the conclusions in an understudied area of ??research.

Lead author Alexandra White, a cancer epidemiologist at the National Institutes of Health who led the study, told AFP that it arose from her previous research that found a link between permanent hair dye and straighteners and breast and ovarian cancer.

“We know that these straighteners contain many different chemicals, including endocrine disruptors, and we would expect them to have adverse health effects from hormone-sensitive cancers,” she said.

“That prompted us to expand our previous work and focus only on uterine cancer.”

Cervical cancer accounts for three percent of all new cancers, but is the most common cancer of the female reproductive system, with more than 65,000 new cases and 12,500 deaths in 2022.

The outlook is generally good if the cancer is caught early, but treatment often involves removing the uterus, which would rule out pregnancy.

The new paper draws on data from more than 33,000 U.S. women ages 35 to 74 who took part in the Sister Study, which is run by the government and designed to identify risk factors for cancer and other diseases .

Over the course of 11 years, 378 women were diagnosed with uterine cancer, which mainly affects the lining of the womb, the endometrium. Type 1, the most common form of cancer, is believed to be related to an excess of the sex hormone estrogen.

Women who reported using hair straightening products in the past year were almost twice as likely to develop cervical cancer as women who never used them, the researchers found.

Connection was even stronger for frequent users – defined as more than four uses in the last 12 months. These women were about 2.5 times more likely to get cancer compared to women who never used the products.

No similar associations were found for other hair products, including dyes, bleaches, highlights, or perms.

“The concern is that these products contain chemicals that essentially act like estrogen in the body,” White said, disrupting normal hormonal processes that could affect cancer risk.

A second possibility is that some products contain carcinogens such as formaldehyde to break the bonds between keratin proteins in the hair, altering its structure and making it smooth.

Although women in the study weren’t specifically asked what products they use, a specific keratin treatment known as “Brazilian blowouts” was popular at the time the women were enrolled in this study between 2003 and 2009, despite its use has since declined.

White said one of the study’s strengths is that it surveyed women about the products years before they actually developed cancer, limiting the possibility of people misremembering or misattributing their exposures.

A key limitation, however, was that they were unable to gather information about the types of hair straighteners used or specific brands, which would have further strengthened the evidence.

White said more laboratory work should be done to examine the proposed ways the chemicals cause cancer, as well as more population studies that recruit racially diverse populations and gather information about brands.

A related comment in the journal acknowledged some shortcomings but said the study adds to a “growing body of evidence” that “hair straightening products are associated with hormone-related cancers in women” and called for evidence-based policy changes.

It added that the personal care products industry upholds Eurocentric “racist beauty standards” and persistently fails to adhere to transparency on chemical ingredients and formulations.