THE HEADLINES ARE FRIGHTENING: “Hair-straightening chemical products linked to increased uterine cancer risk in a new study,” blares CNN. NBC News offers this: “Chemical hair straighteners linked to [a] higher risk of uterine cancer for Black women, study shows.”

Scientists are reporting new details about the association between certain hair straightening products (such as chemical relaxers and pressing products) and increased cancer risk in women.

How concerned should we be? Today we explore the epidemiology of uterus (endometrial) cancer before turning to the magnitude of the risk associated with using hair straightening products.

Uterus cancer basics

Endometrial cancer is a cancer type that begins in the uterus’s inner lining. The uterus is the pear-shaped, hollow pelvic organ in which fetal development occurs.

Endometrial (uterus) cancer start in cells forming the uterus lining. Other cancer types can begin in the uterus, including uterine sarcoma. These other types are much less common than endometrial carcinoma, however.

Fortunately, when it occurs, endometrial cancer is often caught at an early stage, as the disease frequently produces abnormal vaginal bleeding. When discovered early, surgically removing the uterus is often associated with a cure.

Uterus cancer symptoms and risk factors

Endometrial cancer symptoms can include vaginal bleeding after menopause, bleeding between periods, or pelvic pain.

Let’s turn to some factors that can increase the risk of endometrial cancer. The Mayo Clinic (USA) explains that risk factors include:

• Changes in female hormone balance. The ovaries make two “female” hormones — estrogen and progesterone. Fluctuations in the balance of these hormones lead to changes in the uterus lining or endometrium.
• A condition that increases your body’s estrogen (but not progesterone) levels. For example, obesity, diabetes, irregular ovulation patterns, and polycystic ovary syndrome raise endometrial cancer. Taking hormones after menopause that contain estrogen — but don’t include progesterone — increases uterine cancer risk.
• A rare type of ovarian tumor that releases estrogen also can increase the risk of endometrial cancer.
• More years of menstruation. Starting menstruation early — before age 12 — or beginning menopause later increases endometrial cancer risk. The more periods you have experienced, the more exposure your endometrium has had to estrogen.
• Never having been pregnant.
• Older age. With increasing age, endometrial cancer risk rises. Endometrial cancer occurs most often after menopause.
• Obesity. The increase in risk may be secondary to excess body fat altering your body’s hormone balance.
• Hormone therapy for breast cancer. Taking tamoxifen, an anti-hormone drug for breast cancer can increase the risk of endometrial cancer. For most, the tamoxifen benefits outweigh the small risk of endometrial cancer.
• An inherited colon cancer syndrome. Lynch syndrome (hereditary nonpolyposis colorectal cancer (HNPCC)) increases malignancy risk, including colon and uterus cancer. Lynch syndrome is the product of genetic mutations passed from parents to their children. If your family member has been diagnosed with Lynch syndrome, please discuss your risk of the genetic syndrome with your healthcare provider. If you have Lynch syndrome, ask what cancer screening tests you should consider.

Hair straightening and cancer

Many hair products contain endocrine-disrupting compounds and cancer-causing substances that may raise malignancy risk, including breast and ovarian cancer. Products used predominately by Black women may contain more hormonally-active compounds.

Some, but not all, research studies suggest hair dyes and straightener use raise breast cancer risk. But what about uterus cancer?

A new study published in the Journal of the National Cancer Institute discovered:

Among women who did not use hair-straightening chemical products in the past year, 1.6 percent developed uterine cancer by age 70. Approximately four percent of the women who frequently (more than four times in the previous year) used such hair-straightening products developed uterine cancer by age 70.

While more than doubling uterus cancer risk sounds disturbing, the relative increase translates to an absolute increase of just over two percent. While hair straightening products appeared linked to uterus cancer, other hair products — such as perms, dyes, and body waves — did not.

The recent study includes data on nearly 34,000 women in the United States aged 35 to 74. All completed questionnaires about their use of hair products such as dyes, perms, relaxers, and straighteners. The National Institutes of Health researchers also tracked cancer diagnoses.

The association between hair straightening product use and uterine cancer may have the biggest implications for Black women. These women represented only about seven percent of the study population, but 60 percent of those who reported ever using straighteners.

While the researchers did not collect hair product ingredient information, they observed that several chemicals in straighteners might contribute to an increased incidence of uterine cancer.

Speaking to CNN, Harvard T.H. Chan School of Public Health epidemiologist Dr. Tamarra James-Todd observes that some substances found in hair-straightening products, especially those most used by and marketed to Black and Latina women, are hormone-disrupting chemicals.

Hair straighteners and uterus cancer — My take

This research investigation is the first epidemiologic study that examined the relationship between straightener use and uterine cancer.

While the study is provocative, suggesting an association between straightening chemical products and increased uterine cancer risk, it cannot determine that the products cause cancer. It could be pure association.

However, conducting a randomized trial of 40,000 individuals is not practical. I hope we see more research investigations to confirm the findings in various populations and to identify any carcinogens in the products.

Uterine cancer represents three percent of all new cancer cases in the United States but is the most common cancer of the female reproductive system, with 65,950 estimated new cases in 2022. The incidence of uterine cancer has been rising in the United States, especially among Black women.

Endometrial cancer risk reduction

To drop your endometrial cancer risk, you may wish to consider the following:

• Talk to your doctor about the risks of hormone therapy after menopause. Chat with your doctor about the risks and benefits if you’re considering hormone replacement therapy to help control menopause symptoms. Unless you’ve undergone a hysterectomy (uterus removal), estrogen hormone replacement alone after menopause may increase your risk of endometrial cancer. Taking both estrogen and progestin may drop this risk. Hormone therapy has other risks, so weigh the benefits and risks with your doctor.
• Consider taking birth control pills. The risk reduction may last several years after you stop taking oral contraceptives. Of course, oral contraceptives can have side effects, so please discuss the benefits and risks with your doctor.
• Maintain a healthy weight. Obesity increases endometrial cancer risk. If you want to lose weight, increase your physical activity and reduce the number of calories you consume daily.

Thank you for joining me in examining the association between hair straightening product use and uterus (endometrial) cancer risk. Whether you use hair straightening products or not, you may reduce your risk with the strategies described above.