Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women

The “Sister Study Cohort”. This study enrolled 50,884 American women age 35-74. These women did not have a history of breast cancer but had at least one sister who had been diagnosed with breast cancer.

These women were followed for several years and when a diagnosis of breast cancer was made, it was confirmed by the study leaders..

Characteristics and Confounding factors that I found particularly interesting were that 61% of the women were over weight, 45% were previous or current smokers, and 63% were post-menopausal. Women in these groups have a higher risk of breast cancer at baseline.

Specific findings of interest are that in Black women, any permanent dye use in the 12-months before enrollment in the study was associated with a 45% higher breast cancer risk. 74.1% of Black women reported use of hair straighteners compared to 3% of non-Hispanic white women. Use of hair straighteners was associated with 18% higher breast cancer risk (but up to 31% higher risk if frequency of use was every 5-6 weeks).

Why is the risk so much higher in Black women? The authors state that there are higher concentrations of estrogens and endocrine disrupting compounds found in hair products that are marketed to Black women. Also, permanent hair dyes have higher concentrations of aromatic amines, which are known carcinogens. Finally, keep iin mind that Brazilian keratin treatments contain formaldehyde, another known carcinogen.