“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.