Women who use chemical hair-straightening products may be at higher risk for uterine cancer than women who don’t, according to a new large study from the National Institutes of Health (NIH).
Study participants who reported frequent use of hair-straightening products, defined as more than four times in the previous year, were more than twice as likely to go on to develop uterine cancer as those who did not use the products. The findings were published October 17 in the Journal of the National Cancer Institute.
“This doubling rate is concerning,” said the lead author, Alexandra White, PhD, the head of the NIEHS Environment and Cancer Epidemiology group in Research Triangle Park, North Carolina, in a press release. “It is important to put this information into context — uterine cancer is a relatively rare type of cancer.”
Unlike Many Other Cancers, Uterine Cancer Rates Are Rising in the U.S.
Uterine cancer occurs when malignant (cancer) cells form in the tissues of the endometrium, which is the lining of the uterus. It accounts for about 3 percent of all new cancer cases, according to the National Cancer Institute, but it’s the most common cancer of the female reproductive system, with 65,950 estimated new cases in 2022.
Unlike those of many cancers, the incidence and death rates for uterine cancer are rising. New cases have risen by 0.6 percent per year from 2010 to 2019, and death rates have risen an average of 1.7 percent per year during the same time frame.
Previous Research Has Linked Some Types of Hair Products With Breast and Ovarian Cancer
Certain hair products, such as hair straighteners and some dyes, have been associated with hormone-sensitive cancers, including breast and ovarian cancers, according to the authors. Previous research uncovered a link between the use of straighteners and a higher ovarian cancer incidence, but this is the first study to look at how the products could impact the risk of uterine cancer.
Women Who Used Hair-Straightening Products Frequently Were at Higher Risk for Uterine Cancer
The 33,497 participants in the trial were part of the Sister Study, a cohort that included women ages 35 to 74 years old who were breast-cancer free when the study began and had at least one sister diagnosed with breast cancer.
Participants were an average age of 58; 85.6 percent were white, 7.4 percent were Black, and 4.4 percent were Hispanic.
At the beginning of the study, all the women completed an interview and a questionnaire that included questions about the use of different hair products such as hair straighteners, relaxers, and permanent and semi-permanent hair dyes.
The women were followed for almost 11 years, and during that time 378 uterine cancer cases were diagnosed.
The researchers found that women who reported frequent use of hair-straightening products, defined as more than four times in the previous year, were more than twice as likely to go on to develop uterine cancer as those who did not use the products.
“We estimated that 1.64 percent 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 percent,” said Dr. White.
The Overall Risk of Uterine Cancer Is Still Low
The Sister Study is a large, well-designed cohort study, and the authors conducted a rigorous analysis to test this association, says Ashley Felix, PhD, MPH, a researcher who studies uterine cancer and healthcare disparities at the Ohio State University Comprehensive Cancer Center in Columbus but was not involved in the new study. “These findings should certainly be communicated to consumers,” she adds.
“Although no prior study has specifically evaluated the relationship between hair-straightener use and uterine cancer, these findings parallel other analyses that examine the association between hair straightener use and risk of breast and ovarian cancers, providing biological plausibility,” says Dr. Felix.
As the authors mention, this does not translate to a large absolute increase in risk, she notes. “So, while the risk is doubled, the absolute risk of developing uterine cancer in either group is still low. This is because uterine cancer is a relatively rare cancer,” she says.
Hair Dyes, Bleach, Highlights, or Perms Were Not Associated With a Higher Risk of Uterine Cancer
The researchers found no associations with uterine cancer for other hair products that the women reported using, including hair dyes, bleach, highlights, or perms.
The researchers did not collect information on brands or ingredients in the hair products the women used. But several chemicals that have been found in straighteners (such as parabens, bisphenol A, metals, and formaldehyde) may be contributing to the increased uterine cancer risk observed, the authors wrote.
Researchers believe that chemical exposure from hair product use, especially straighteners, could be more concerning than other personal care products because of increased absorption through the scalp, which may be exacerbated by burns and lesions caused by straighteners.
Black Women May Be at Higher Risk Because of Frequency of Use
Approximately 60 percent of the participants who reported using straighteners in the previous year self-identified as Black women. Although the study did not find that the relationship between straightener use and uterine cancer incidence was different by race, the adverse health effects may be greater for Black women.
“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, PhD, an author of the new study and a research fellow in the NIEHS Epidemiology Branch, in the release.
Black Women Are at Higher Risk for Uterine Cancer
Black women in particular have a higher risk of developing aggressive endometrial cancer subtypes (called Type II in the study), and recent data shows that the risk of developing less-aggressive subtypes is also increasing among Black relative to white women, says Felix.
In a study published May 22, 2019, by the NIH, researchers found that aggressive, nonendometroid subtypes of uterine cancer had been increasing dramatically in all racial or ethnic groups, and increasing at a much higher rate in Black women than in all other races or ethnic groups.
“Unfortunately, the study was unable to examine the relationship between hair-straightener use and risk of Type II (aggressive) uterine cancer due to small numbers. If we were to see a strong association with hair-straightener use and risk of Type II uterine cancer, it might suggest one avenue by which Black women are more likely than white women to develop these aggressive tumors, given their higher prevalence of use,” says Felix. Because of this limitation, the findings don’t really improve on our understanding about the known treatment disparities that are present for uterine cancers, she adds.
Should Women Be Cautioned About Using Hair Straighteners?
Since this is the only study to look at the association between hair-straightener use and uterine cancer risk, we would want to see these results replicated in independent studies in order to have stronger evidence of a link, says Felix.
“That said, the results from this study along with the scant studies conducted for breast and ovarian cancer suggest that something is going on in terms of hair straightener use and risk of certain cancers. I do think women should know about these associations, but in terms of ‘warning’ women, the evidence is still in its infancy,” she says.
White said, “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.”