Eberle CE, Sandler DP, Taylor KW, et al. Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women. Int J Cancer 2020; 147(2):383-391. https://pubmed.ncbi.nlm.nih.gov/31797377/

Hair dye use is common in adult women with more than 1/3 of women in the United States (US) over the age of 18 using hair dye. It is known that hair dye contains many chemicals, including some that have mutagenic and endocrine disrupting properties. Some of the aromatic amines seen in hair dye have been shown to stimulate breast tumors in rats. In addition, chemical relaxants and straighteners contain a mixture of chemicals, including formaldehyde, which is known to cause cancer. Prior studies had been relatively inconclusive regarding the role of hair dyes and breast cancer risk; however, many were retrospective and predominantly included only white women.

The Sister Study cohort prospectively enrolled over 50,000 women in the US between 2003 and 2009. These women had no personal history of breast cancer but had at least one sister diagnosed with breast cancer. Women reported their breast history as well as hair dye and straightener use over 8 years after enrolling in the study. Over half of the women had used hair dye in the 12 months prior to enrolling in this study.

The Sister Study cohort found that women who used permanent hair dye and chemical straighteners or applied it to others were at a higher risk of breast cancer. Interestingly, only a 9% increased risk of breast cancer was seen when looking across all races and ethnicities. However, black women who used permanent hair dye had a 45% increased risk of breast cancer. There was no increased risk of breast cancer seen for semi-permanent or temporary hair dye use. Women who used hair straighteners at least every five to eight weeks were about 30% more likely to develop breast cancer, and this association between straightener use and breast cancer was similar in African American and white women.

It is important to remember that all women enrolled in the trial had a family history of breast cancer by the trial design. However, the association of increased risk of breast cancer with the use of permanent dyes and straighteners remains. While permanent dye use was associated with an increased risk of breast cancer, light-colored hair dye was associated with a higher risk of breast cancer compared to a dark-colored hair dye. Home application of hair dye also showed a higher risk of breast cancer compared to hair dye applied in the salon.

What does this mean for our hair? There are many things we can do to lower our risk of breast cancer in our environment. These include keeping a healthy weight, exercising, and decreasing our lifetime risk of estrogen exposure. Understanding what items in our environment may increase your risk of breast cancer such as permanent hair dyes and straighteners is important. Increased frequency of use and light hair dye colors seem to convey an increased risk. Therefore, knowing family history and personal risk factors can help inform the decisions we choose.