CHICAGO – A new report links hair straightening products with an increased risk of uterine cancer.

Researchers with the National Institutes of Health studied eleven years of data from more than 33-thousand women between the ages of 35 and 74 participating in the Sister Study, which aims to identify risk factors for breast cancer and other health conditions.

Researchers discovered women who used straightening products more than four times in a year, more than doubled their chances of developing uterine cancer compared to women who didn’t use the products.

“This doubling rate is concerning.” said Alexandra White, Ph.D., head of the NIEHS Environment and Cancer Epidemiology group and lead author on the new study, in a news release. “However, it is important to put this information into context – uterine cancer is a relatively rare type of cancer.”

The NIH says uterine cancer is the most common cancer of the female reproductive system and accounts for 3% of all new cancer cases.

It’s estimated there will be 65,950 new cases this year, and studies show incidence rates rising among women in the United States, especially Black women.

In fact, approximately 60% of the women in the study who self-identified as black reported using straighteners in the previous year.

Researchers say while the study didn’t find the relationship between straightener use and incidences of uterine cancer was different in terms of race, they do believe it may be higher among black women due to a “higher prevalence of use.”

“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,” said Che-Jung Chang, Ph.D., author on the new study and research fellow in the NIEHS Epidemiology Branch, in a news release.

Researchers did not give specific information on brands but did say chemicals found in straighteners such as parabens, bisphenol A, formaldehyde and metals can increase risks for uterine cancer because they can be absorbed through the scalp,  burns, or lesions caused by the straighteners.

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

Researchers say they did not find any uterine cancer risks associated with other hair products such as hair dyes, bleach, highlights and perms.

The same team previously found that permanent hair dye and straighteners may increase breast and ovarian cancer risk.