Hair straightening chemicals linked to uterine cancer risk

Uterine cancer is known to be one of the most common gynecologic cancers. There has been an increase in the mortality and incidence rates in the US over the past two decades resulting in more than 65,950 new cases and 12,550 deaths expected in 2022. Excess exposure to estrogen and the hormonal imbalance of progesterone and estrogen has been reported to be significant risk factors for uterine cancer. Therefore, synthetic estrogenic compounds such as endocrine-disrupting chemicals (EDCs) are suggested to increase uterine cancer risk since they can alter hormonal actions.

The use of various EDCs in hair products has been linked to hormone-sensitive cancers, such as ovarian and breast cancer. In addition, the constituents of hair products, such as formaldehyde-releasing chemicals and formaldehyde in hair straighteners, as well as 4-aminophenyl and phenylenediamine, may also contribute to cancer development.

Studies have shown that more than half of women in the United States and Europe use permanent hair dyes. A previous Sister Study showed a higher rate of breast cancer incidence among adults and adolescents who use hair products and a high rate of ovarian cancer incidence among adults who use straighteners. However, the impact of the use of hair products on uterine cancer has not been determined yet.

A new study in the Journal of the National Cancer Institute aimed to analyze the association of hair product use with age-specific uterine cancer in a large, ethnically, and racially diverse population in the United States.

Study: Use of Straighteners and Other Hair Products and Incident Uterine Cancer.  Image Credit: Kateryna Kon / ShutterstockStudy: Use of Straighteners and Other Hair Products and Incident Uterine Cancer.  Image Credit: Kateryna Kon / Shutterstock

About the study

The study involved only breast cancer-free women in the United States, aged between 35 and 74 years, and at least one sister diagnosed with breast cancer. All participants had to complete an interview and questionnaires on the use of hair products at baseline. The height and weight of the participants were also measured during home visits at baseline. Additionally, participants or next of kin (for deceased participants) were followed up annually concerning any new cancer diagnoses or other health-related changes. They were followed up in more detail every 2 to 3 years.

Women with a self-reported diagnosis of uterine cancer before enrolment, uncertain timing of diagnosis, uncertain uterine cancer history, hysterectomy before enrolment, no answers to hair product use questions, and no contribution to follow-up time were withdrawn from the study.

Information on the frequency of personal use of 7 hair products, including temporary, semi-permanent, and permanent hair dyes, highlights, bleach, relaxers, straighteners, or pressing products, as well as body waves or hair permanents, was obtained from all eligible participants. The response options were “1-2 times per year”, “every 5-8weeks”, “every 3-4months”, “did not use,” and “once per month.” In addition, information on the frequency of nonprofessional application of others was obtained for semi-permanent hair dyes, permanent hair dyes, relaxers, straighteners, or pressing products. Information on the lifetime duration of use and color of dyes were obtained for permanent and semi-permanent dye use. Furthermore, women who reported a cancer diagnosis had to provide authorization to use medical records for confirmation.

The confirmed uterine cancer cases were then classified as endometrial cancers and further defined as type I and type II endometrial cancer. Other data collected at baseline included age, physical activity, ethnicity and race, smoking status, alcohol consumption, reproduction history, educational qualification, occupational history, hormone replacement therapy use, and oral contraceptives. Finally, the body mass index (BMI) was calculated from the obtained height and weight at baseline.

Study findings

The results indicated that the participants comprised 7.4% Black/African American, 85.6% non-Hispanic White, 4.4% Hispanic/Latina non-Black, and 2.5% of all other ethnicities and races. They reported a high educational qualification and uterine cases common for those older with an earlier menarche age, lower physical activity, and higher body mass index (BMI). The participants who used straighteners were observed to be predominantly African American/Black, had lower physical activity, higher BMI, and were younger.

“We estimated that 1.64% 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%,” said Alexandra White, Ph.D., head of the NIEHS Environment and Cancer Epidemiology group and lead author on the new study. “This doubling rate is concerning. However, it is important to put this information into context - uterine cancer is a relatively rare type of cancer.”

Frequent straightener use was reported to be associated with a higher risk of uterine cancer. Moreover, infrequent use was also associated with an elevated risk of uterine cancer. Approximately 1.64% of women who never used straighteners 12 months before baseline were assumed to develop uterine cancer by 70 years of age. This estimated risk was 1.18% higher for women with infrequent use and 2.41% higher for women with frequent use. However, using other hair products were not observed to be associated with a higher risk of uterine cancer. Additionally, these higher rates were reported to be similar for postmenopausal and endometrial cancer cases and medically confirmed uterine cancer cases.

“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, Ph.D., an author on the new study and a research fellow in the NIEHS Epidemiology Branch.

Furthermore, women with low levels of physical activity were observed to be more strongly associated with using straighteners than those with high levels of physical activity. However, no association was observed between race, ethnicity, or obesity and the use of straighteners. Moreover, no effect of obesity, race, physical activity, or ethnicity was observed using hair permanents, semi-permanent dyes, or permanent dyes.

Therefore, the current study demonstrated that using hair straightening products can increase the risk of uterine cancer. Further research is required to confirm such findings and evaluate the role of hair products in uterine cancer. However, the findings of this study can be used as a potential target for intervention that will help against the rising incidence of uterine cancer cases and extensive use of hair products.

“To our knowledge this is the first epidemiologic study that examined the relationship between straightener use and uterine cancer,” said White. “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.”


The study has certain limitations. First, the specific chemicals that contribute to uterine cancer were not identified. Second, self-reporting of the use of hair products leads to exposure to previously unidentified chemical mixtures. Third, the evaluation of exposure took place 12 months before baseline, although product formulations and use behaviors can change over that time. Finally, the use of straightening products also included pressing products that might impact the relationship between relaxers, chemical straighteners, and uterine cancer.

Journal reference:
Suchandrima Bhowmik

Written by

Suchandrima Bhowmik

Suchandrima has a Bachelor of Science (B.Sc.) degree in Microbiology and a Master of Science (M.Sc.) degree in Microbiology from the University of Calcutta, India. The study of health and diseases was always very important to her. In addition to Microbiology, she also gained extensive knowledge in Biochemistry, Immunology, Medical Microbiology, Metabolism, and Biotechnology as part of her master's degree.


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