Permanent hair dyes and chemical hair straighteners increased the risk of breast cancer, particularly in black women, according to a study published in the International Journal of Cancer.
This national prospective cohort study assessed the use of hair dye and chemical relaxer/straightener and breast cancer risk by ethnicity. The study included women without breast cancer participating in the Sister Study (n=46,709) who were 35 to 74 years, were enrolled between 2003 and 2009, and had a sister with breast cancer.
Participants completed questionnaires about their past 12‐month hair product use. More than half of participants (55%) reported using permanent dye at enrollment.
Breast cancer risk more substantial in black women
After 8.3 years of follow-up, there were 2,794 breast cancer diagnoses. Use of permanent hair dye was associated with a 45% increased risk of breast cancer in black women (hazard ratio [HR] = 1.45; 95% CI, 1.10-1.90) compared with a 7% increased risk in white women (HR=1.07; 95% CI, 0.99-1.16; P=0.04).
The risk of breast cancer was even greater for patients who regularly used permanent hair dye: use every five to eight weeks was associated with a 60% (HR=1.6; 95% CI, 1.11-2.3) increased risk in black women and an 8% (HR=1.08; 95% CI, 0.98-1.18) increase in white women.
Use of chemical relaxer/straightener was associated with breast cancer risk for all participants (HR=1.18; 95% CI, 0.99-1.41), and increased frequency of use was associated with a higher risk of breast cancer (P=0.02). Again, black women were more significantly impacted than white women (74.1% vs. 3.0%, respectively).
Non-professional application of semi-permanent hair dye (HR=1.28; 95% CI, 1.05-1.56) and straighteners (HR=1.27; 95% CI, 0.99-1.62) was also associated with an increased breast cancer risk.
“These results suggest that chemicals in hair products may play a role in breast carcinogenesis,” the researchers concluded.