- A prospective cohort of women whose sister had breast cancer finds increased risk of developing breast cancer associated with use of permanent hair dyes and chemical straighteners.
- Black women using permanent hair dyes had up to 60% increased risk of developing breast cancer.
Why this matters
- Use of permanent dyes is highly common, with 55% of cohort using them.
- Hair products are known to contain endocrine-disrupting chemicals and carcinogens in animal studies.
- Prospective cohort (n=46,709; aged 35-74 years) known as the Sister Study was of women free of breast cancer at enrollment but whose sister had breast cancer.
- Funding: NIH.
- Follow-up mean was 8.3 years.
- Permanent hair dye (any use vs nonuse):
- All women: HR, 1.09; 95% CI, 1.01-1.17.
- White women: HR, 1.07; 95% CI, 0.99-1.16.
- Black women: HR, 1.45; 95% CI, 1.10-1.90.
- Black women with use every 5-8 weeks: HR, 1.60; 95% CI, 1.11-2.30.
- Personal chemical straightener (any use vs nonuse):
- All women: HR, 1.18; 95% CI, 0.99-1.41.
- No differences by ethnicity.
- Increased frequency of use carries higher risk (Ptrend=.02).
- Observational design.
- Individual chemical constituents not studied.