Publisher Health

Women who use chemical hair straighteners frequently could have a higher risk of developing uterine cancer than women who have never used the products, according to new findings from a national study that has followed nearly 34,000 U.S. women for more than a decade.

The study did not establish a cause-and-effect relationship between hair straighteners and cancer of the uterus, a form of reproductive cancer that has been increasing in incidence among women in recent years, especially among Black women.

For women in the study who had never used hair straighteners, the risk of developing uterine cancer by the age of 70 was 1.64 percent, the research found, while the rate for frequent users of straighteners was more than doubled at 4.05 percent.

While the increased risk was found among women from all racial and ethnic backgrounds, Black women might be disproportionately affected: Sixty percent of participants who reported using hair straighteners self-identified as Black women, according to the study.

It defined frequent use as more than four times in the previous year, and included any personal use, whether women applied products themselves or had the straighteners applied by others.

“We don’t want to panic people,” said Alexandra White, head of the environment and cancer epidemiology group of the National Institute of Environmental Health Sciences (N.I.E.H.S.) and the study’s lead author. “One could make a decision to reduce this chemical exposure, but we also want to acknowledge that there is a lot of pressure on women, especially Black women, to have straight hair. It’s not an easy decision to not do this.”

The research, using data from the institute’s Sister Study, appears to be the first epidemiological study to report a link with uterine cancer, but researchers cautioned that the findings need to be confirmed with more study. Hair straightener use has also been tied in previous studies to a higher risk of ovarian and breast cancers.

Published Monday in The Journal of the National Cancer Institute, the study did not find a link between uterine cancer and other hair products using chemicals for dyes or coloring, bleach, highlights or perms.

Rates of uterine cancer have been rising recently among all women in the United States, but Black women die of uterine cancer at twice the rate that white women do, according to a report from an expert panel in March. The gap is one of the largest racial disparities reported for any cancer.

“We’ve seen this association between hair straighteners and breast, ovarian and now uterine cancer — it’s been a consistent finding among hormonally driven female reproductive cancers,” Dr. White said.

The researchers did not gather information about the brands or the ingredients in the hair products used by study participants. But they noted in the paper that several chemicals that have been found in straighteners, such as parabens, bisphenol A, metals and formaldehyde, could play a role in the increased uterine cancer risk, and that some of those chemicals have endocrine-disrupting properties. Chemical exposure from hair products like straighteners could be more concerning than other personal care products because of the potential for increased absorption through the scalp, which burns and lesions caused by straighteners could exacerbate.

Hair products and other cosmetics do not need approval by the Food and Drug Administration to be sold. Companies and product manufacturers are legally responsible for ensuring the safety of their products, but they are not required to test either the products or their ingredients for safety.

As part of the study analysis, the scientists made adjustments for other factors that could impact cancer risk, such as body mass index, physical activity, menopausal status, smoking, alcohol use and use of hormones for contraception or replacement therapy. Women who worked in beauty salons or barbershops were excluded from the analysis to eliminate the possibility of occupational exposures affecting the study’s results. Women with uterine cancer tended to be older with an earlier age of menarche, or onset of menstruation, a higher body mass index and lower physical activity.

Women who had used hair straighteners infrequently also had an increased risk of developing uterine cancer, but that was not statistically significant and could have been a chance finding, according to the study.

Uterine cancer is increasing rapidly. The number of cases diagnosed each year has risen to 65,950 this year from 39,000 just 15 years ago.

The Sister Study cohort includes 50,884 women aged 35 to 74 who had at least one sister with breast cancer but were themselves breast cancer-free when they enrolled in 2003-9. Some 7.4 percent were Black, 4.4 percent were Hispanic, 85.6 percent were white, and 2.5 percent were of other races and ethnicities. Some 15,585 of the participants who had undergone hysterectomies before enrolling were not included in this analysis, which looked at 378 uterine cancer cases identified over the nearly 11 years of follow-up.

Prominent early warning signs of uterine cancer include regular spotting in between periods and changes in menstrual bleeding, before or after menopause, as well as pelvic pain and painful urination and intercourse. When detected early, overall survival rates are high.

But the mortality rate has been increasing by almost 2 percent a year overall, with even sharper spikes among Asian, Hispanic and Black women, according to a recent study in JAMA Oncology.

And though it more often occurs after the age of 50, more women are being diagnosed at younger ages than in the past, often while still in their childbearing years.