Chemical Straighteners and Permanent Hair Dyes May Increase Breast Cancer Risk

A study published in the International Journal of Cancer suggested that there is a correlation between breast cancer risk and the use of chemical straighteners and permanent hair dye, especially among black women.¹

Separate evaluation results between white and black women highlighted potential differences in associations by ethnicity. These findings have the potential for significant public health impact given the commonality of hair dye and chemical straightener use.

“Our finding is the first estimate of the association between straightener use and breast cancer from a prospective cohort that assessed exposure after the introduction of formaldehyde-containing straighteners to U.S. markets,” the researchers wrote.

In this cohort of 46,709 sister study participants in which participants had a sister with breast cancer but were cancer-free themselves, permanent hair dye use was associated with a 45% higher breast cancer risk in black women (HR, 1.45; 95% CI, 1.10-1.90), and a 7% higher risk in white women (HR, 1.07; 95% CI, 0.99-1.16; heterogeneity P = .04). Among all participants, personal straightener use was associated with breast cancer risk (HR, 1.18; 95% CI, 0.99-1.41), and higher risk was associated with increased frequency (p for trend = .02).

The association with permanent dye use among black women was evident for both dark-colored dye (HR, 1.51; 95% CI, 0.91-2.34) and light-colored dye (HR, 1.46; 95% CI, 0.91-2.34). Among white women, breast cancer risk was associated with use of light-colored permanent dye (HR, 1.12; 95% CI, 1.01-1.23), but not dark-colored permanent dye (HR, 1.04; 95% CI, 0.94-1.16).

Chemical straightener use (9.9% of participants) varied by ethnicity, with 74.1% of black women reporting any use compared to 3.0% of non-Hispanic white women. A higher risk was evident for nonprofessional application of straighteners to others (HR, 1.27; 95% CI, 0.99-1.62). Overall, straightener use in the 12 months before enrollment was associated with an 18% higher risk of breast cancer (95% CI, 0.99-1.41).

“Hair product constituents vary depending on whether they are marketed to black or white women; studies suggest that products designed for use by black women may contain more endocrine-disrupting chemicals. Additionally, personal care product use patterns vary by ethnicity and thus differences in exposure to chemicals through hair products may contribute in part to racial disparities in breast cancer incidence,” the researchers wrote.

A higher risk of premenopausal breast cancer was associated with light dye use (HR, 1.30; 95% CI, 1.04-1.62). The association for non-professional application of semi-permanent dyes (HR, 1.35; 95% CI, 1.08-1.69), and personal use (HR, 1.26; 95% CI, 1.02-1.55) and application to others (HR, 1.34; 95% CI, 0.99-1.79) of straighteners was most evident for postmenopausal breast cancer.

Researchers indicated that future studies that evaluate the possibility of differences by ethnicity and tumor subtype are needed.

According to the National Cancer Institute, it is estimated that more than one-third of women over age 18 and 10% of men over age 40 use some type of hair dye, and over 5,000 different chemicals are used in hair dye products, some of which are reported to carcinogenic in animals.²

References:
1. Eberle CE, Sandler DP, Taylor KW, White AJ. Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women. International Journal of Cancer. doi:10.1002/ijc.32738.
2. National Cancer Institute. Hair Dyes and Cancer Risk. National Cancer Institute website. Published August 18, 2016. cancer.gov/about-cancer/causes-prevention/risk/myths/hair-dyes-fact-sheet. Accessed December 4, 2019.