Study: Hair straightening products linked to small increased risk of endometrial cancer

IN-DEPTH REVIEW OF RESEARCH

Researchers of this study wanted to know

Some hair products contain chemicals that mimic certain hormones that promote the growth of hormone-sensitive cancers. Using these products can increase the risk for certain cancers, especially hormone-sensitive cancers. In this study, the researchers wanted to better understand if hair straighteners, relaxers, pressing products, permanents or body waves were linked to an increase in endometrial (uterine) cancer, which is the most common gynecologic cancer.

Populations looked at in this study

The Sister Study is a prospective cohort that enrolled 50,884 women between 2003-2009. Participants were eligible if they were women between ages 35 to 74 who were free of breast cancer, lived in the United States (including Puerto Rico) and had at least one sister diagnosed with breast cancer.

For this study, researchers excluded women who withdrew their participation, self-reported a diagnosis of endometrial cancer before enrollment, had an uncertain endometrial cancer history, had an unclear timing of diagnosis relative to enrollment, had a hysterectomy before enrollment, did not answer any hair product use questions or did not contribute any follow-up time. As a result, the study included 33,947 eligible women. Many participants had a college degree or higher level of education (56%).

Study design

Participants were asked questions about their use of hair products in the prior month.  This included questions about how frequently they used hair dyes; straighteners, relaxers, or pressing products; and permanents or body waves. Use was self-reported and was not verified by researchers.

The researchers followed each participant for 10.9 years on average, from the time of enrollment until an endometrial cancer diagnosis, a loss of follow-up, the end of follow-up or death.

The researchers then estimated the association between hair product use and endometrial cancer incidence. They adjusted these results based on various factors, including race and ethnicity, educational level, BMI, physical activity, menopausal status at enrollment, whether participants had given birth or never given birth, smoking status, alcohol consumption, oral contraceptive use and duration, use of hormone replacement therapy and age at first menstrual period.

Study findings

• The endometrial cancer cases that were diagnosed over the course of the study tended to occur among older women with an earlier age of first period, a higher BMI and lower physical activity.
• The participants who had ever used straighteners were mostly Black (60%) and tended to be younger with a higher BMI and lower level of physical activity than those who had never used hair straighteners.
• The risk of endometrial cancer was significantly increased among women who had used hair straighteners in the previous 12 months compared to those who never used hair straighteners.
• Compared to no use of straighteners, frequent use (4 or more times per year) was associated with a statistically significantly higher rate of endometrial cancer than those who never used hair straighteners.
• In contrast, the use of other hair products, including permanent hair dye, was not associated with an increased rate of endometrial cancer.
• Researchers observed differences in associations based on physical activity levels and straightener use.
  • Among those who had ever used hair straighteners, there was an increased rate of endometrial cancer in people with low levels of physical activity compared to those with high levels of physical activity.
  • Similar patterns were also observed among people with frequent use, where less physical activity was associated with a higher rate of endometrial cancer.
• Endometrial cancer rates among those who used hair straighteners did not vary by race and ethnicity or obesity. Moreover, there was no difference in cancer rates by physical activity, race and ethnicity, or obesity for use of permanent dyes, semi-permanent dyes, or hair permanents. Few Black women participated in the study, so further research is needed to understand the impact of hair straighteners on endometrial cancer in Black women.
• Participants who had ever used straighteners were mostly Black and tended to be younger with a higher BMI and lower level of physical activity than those who had never used straighteners.

Limitations

• The effect of hair straighteners was based a small number of endometrial cancer cases.
• Uterine cancer often takes years to develop, so use over the past year might not relate to the cancer.
• Several possible other factors including oral contraceptive use and hormone replacement therapy could also affect endometrial cancer rates.
• The study did not include information on cardiovascular disease, which is known to be common in people with endometrial cancer and the primary cause of death for women in the US.

Context

This is the first study investigating the relationship between hair straightener use and endometrial cancer. Previous studies have demonstrated that exposure to hair straighteners was associated with lower sex hormone levels, elevated risk of uterine leiomyomata (benign fibroids), early age at menarche, and increased risk of breast and ovarian cancer, supporting a potential role of hair straighteners in the growth and incidence of hormone-sensitive cancer and other diseases.

Several chemicals that are often identified in hair straighteners could contribute to the increased endometrial cancer rates observed in this study. Concentrations of parabens (preservatives) in endometrium tissues and phthalates (chemicals used to make plastics more durable) in urine samples were higher in participants with endometrial cancer than in those who did not have endometrial cancer. Chronic exposure to low-dose bisphenol A (a chemical used to develop certain plastics) has been associated with altered menstrual cycles and uterine anatomy in rats, which has been associated with endometrial cancer development and progression. Notably, using these chemicals on your scalp is more concerning since the scalp tends to absorb more chemicals than other skin areas. Scalp skin that is heated or burned by the application of hair straighteners may lead to even higher absorption of these chemicals.

Conclusions

In a group of nearly 34,000 people, researchers found an association between the use of hair straighteners and the incidence of endometrial cancer. This is the first study of its kind, and more research is needed to confirm these findings in different populations, particularly in Black people because of the high prevalence of straightener use.

In this study, the observed effects of using hair straightening products on endometrial cancer were very small. In addition, no increase in endometrial cancer was observed with the use of permanent or semi-permanent hair dyes.

Future studies are needed to identify the specific chemical ingredients that contribute to the increase in endometrial cancer rates. Given the widespread use of hair products and the rising incidence of endometrial cancer, these findings are particularly relevant for public health approaches to reduce endometrial cancer incidence.

Share your thoughts on this XRAY review by taking our brief survey.
posted 4/18/23