Over the past decade, evidence has been building that chemical hair straighteners, relaxers and dyes potentially contribute to our risk of developing certain cancers.
Past research has found that hair dyes and straighteners are associated with higher rates of ovarian and breast cancer. Though it’s unclear how these products may contribute to cancer, scientists suspect some chemical ingredients may impair the endocrine system and lead to the formation of cancer cells.
Now, a large study by the National Institute of Environmental Health Sciences is the first to show that these products may increase people’s risk of uterine cancer, too. The research, published Monday in the Journal of the National Cancer Institute, found that the risk of uterine cancer doubled among people who frequently used chemical hair straighteners.
“These findings suggest that [people] should consider their use of hair products in light of the fact that the chemicals in straightening products may influence their risk of developing uterine cancer,” Alexandra White, head of the NIEHS environment and cancer epidemiology group, told HuffPost. “However, the overall risk is not large and chemical hair products are just one of many factors that may influence a woman’s chances of getting uterine cancer.”
What we know about chemical hair products and cancer
For the study, the researchers tracked the health of more than 33,000 women over 11 years. The research team logged how frequently the participants used chemical-based hair products and any health conditions they developed.
Of those who didn’t use chemical hair straighteners in the previous year, 1.6% developed uterine cancer by age 70. About 4% of the women who frequently used chemical hair straighteners (meaning over four times in the previous year) developed uterine cancer — that’s a twofold greater risk. The heightened risk was most pronounced among Black women, already disproportionally impacted by uterine cancer.
This isn’t the first study to link chemical hair products to a higher risk of cancer. A National Institutes of Health study published in 2020 found that people who regularly use chemical hair dyes and straighteners had a greater risk of breast cancer. That study also found that Black women, who tend to use these types of hair products more frequently, were linked to a 45% higher rate of breast cancer, compared with white women who were associated with a 7% higher rate.
In recent years, study after study has similarly associated frequent use of chemical-based hair products with a higher risk of breast cancer, particularly among women of color.
Nicole Deziel, an associate professor of epidemiology and Yale Cancer Center cancer prevention and control member, said the new NIEHS study adds to the growing body of research showing that popular beauty products contain harmful ingredients that may be contributing to increased cancer and other health outcomes.
“Hair-straightening products contain many harsh, toxic and hormone-disrupting chemicals, and because they are left on the scalp for extended periods of time and women may use them repeatedly starting at young ages, this increases the potential for exposure,” Deziel said.
Here’s why these products may lead to cancer
It’s not yet clear how chemical-based hair straighteners contribute to cancer, since the research is still in the early stages, according to Dr. Oliver Dorigo, the director and associate professor of gynecologic oncology at Stanford University.
Many chemical-based straighteners include formaldehyde and formaldehyde-releasing chemicals, which are known carcinogens. But the leading theory is that some of the chemicals, like metals, phthalates and parabens, can disrupt estrogen levels in the body and create hormonal imbalances. We know that excess estrogen is a risk factor for various hormone-influenced cancers, like breast, ovarian and uterine cancer. We also know that the uterus is extremely sensitive to hormonal changes.
“At this point, we may hypothesize that some of the ingredients may have a stimulating effect on the lining of the uterus, called the endometrium, and the endometrium is very responsive to changes in hormone cycles and is particularly responsive to estrogen,” Dorigo said. This may cause the uterine lining to thicken over time, and in certain cases turn into cancer.
Can you tell which products are safest?
Because there’s so little research on the ingredients, it’s too soon to make any firm recommendations. That said, it may be worth scaling back how frequently you use chemical straighteners and relaxers, White said, regardless of whether you use them at home or in the salon. She also encouraged physicians to share these findings with their patients so they can make informed decisions about using chemical hair straighteners.
Most product labels don’t accurately list all of the chemicals included in hair straighteners, so it’s tough to know what’s actually in the products. Deziel said the new study highlights the need for stricter regulatory oversight of these types of products and for safer and affordable alternatives.
In the meantime, the best thing to do is proceed with caution.
“At this point, I think it’s fair to say that this is an association which we have to be aware of — but I wouldn’t draw any other conclusions until further studies show more data, specifically in terms of explaining the causality of the hair straighteners on uterine cancer development,” Dorigo said.
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