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The Impact of Hair Dye and Chemical Straighteners on the Risk of Breast Cancer

An estimated one-third of women above the age of 18 use hair dye. Scientific evidence suggests that hair products contain more than 5000 chemicals, including some that cause mutations and disrupt hormone levels. Research shows that some of the chemicals in hair dye have been detected in breast ductal epithelial cells. Chemical treatments used to straighten or relax hair (straighteners) also contain many chemicals, including formaldehyde, a known carcinogen.

Recent studies reported an excess 25% risk for breast and bladder cancer associated with hair dye use; however, the results have been inconsistent. Far fewer studies have assessed the risk of straighteners used predominantly in African American women. This recent study by researchers at the National Cancer Institute evaluated the association of hair dye and straighteners with the risk of breast cancer. The sample size of women studied was 46,709, with an average follow-up of 8.3 years.

Permanent hair dye use was common, with 55% of women reporting use within the 12 months before enrollment into the study. Compared to women who did not use hair dye, women using dye tended to be younger, had fewer years of education, were more likely to smoke cigarettes, and use oral contraceptives. Both light and dark-colored dye were associated with higher breast cancer risk. The risk increased with increasing frequency of use. The association of hair dye use with breast cancer varied by ethnicity. In Black women, any permanent dye use within the last 12 months of enrollment was associated with a 45% increase in breast cancer risk. Increased frequency of use elevated the risk of breast cancer. Black women who use dye every 5 to 8 weeks had a 60% higher risk of developing breast cancer. The risk of breast cancer was similar in Black women using light and dark-colored dyes. In white women, the risk of breast cancer was increased with light-colored dye, approximately 12%, but not with dark dyes.

The use of straighteners (9.9% of the total) varied by ethnic group, with 74% of Black women reporting use of straighteners compared to 3% of non-Hispanic white women. Straighteners were associated with an 18% higher breast cancer risk. Straighteners were more frequently associated with a higher risk of developing breast cancer. Those who reported using straighteners at least every 5 to 8 weeks had a 31% increase in the risk of breast cancer.

The researchers also noticed a higher risk of breast cancer in premenopausal women associated with light-colored dye. They also noted an increased risk of breast cancer related to the nonprofessional application of hair dye compared with professional dye application.

The authors revealed that the association observed for dye use in Black women was consistent with prior studies that showed higher concentrations of estrogen-disrupting compounds in hair products marketed to Black women. This study was consistent with results reported by the Women’s Circle of Health Study, which observed a similar increase in the use of permanent dark dye among African-American women. In summary, the authors identified a 9% higher breast cancer risk for permanent dye use in all women, but little or no associated risk increase with semipermanent or temporary dye use. The authors also explained the increased risk with the nonprofessional application as follows: the “…at-home kits contain gloves, but potential absorption on hands and forearms, inhalation of toxic chemicals, and residual agents remaining on surfaces are in the air in poorly ventilated settings introduce several mechanisms for exposure.”

The researchers also noted that the formulation of popular straighteners has changed beginning in the early 2000s. Brazilian keratin treatments were introduced at that time, which contained formaldehyde, a known carcinogen or one of its derivatives that reacts with keratin when heated. This study from the National Cancer Institute is the first to estimate the association between the use of straighteners and the risk of breast cancer since the introduction of straighteners containing formaldehyde.

The authors concluded “that as hair dye and straighteners are common exposures, these findings have the potential for substantial public health impact.”