46,709 black and white women were enrolled in the study. The participants aged 35–74 were cancer free at the time of enrolment, but had a sister who had breast cancer. The mean observation time was 8.3 years. 2,794 breast cancers were identified during the study. Permanent dye use was associated with 45% higher breast cancer rates in black women. In white women there were 7% higher breast cancer rates with permanent hair dye use. When women applied semi-permanent hair dyes to their hair this resulted in 28% breast cancer. The use of straighteners was associated with 27% of breast cancer.
Details of the breast cancer study
1. Frequency of applications is important as well. Black women who dyed their hair every 6 to 8 weeks, had a risk of 60% to develop breast cancer than black women who did not dye their hair.
2. This study was a “sister study” where the applicant’s sister had a history of breast cancer. However, the applicant was cancer-free. We know from other studies that immediate female relatives have double the risk to also come down with breast cancer.
3. The hair dyes contain mutagenic and endocrine-disrupting properties such as aromatic amines that could cause breast cancer. 2,4-diaminoanisole sulfate and para-phenylenediamine were causing tumors in the mammary glands with rat experiments.
More evidence of increased breast cancer risk
4. Light-colored hair dyes were associated with 12% breast cancer risk, for dark-colored hair dye it was only 8%. Interestingly, the risk did not vary with years of use. When a salon professional applied semi-permanent hair dye, there was no association with breast cancer risk. However, non-professionals applying semi-permanent dye to others increased the breast cancer risk to 28%. Temporary hair dye application showed no breast cancer risk.
5. Black women had the highest risk of breast cancer after applying permanent hair dyes, namely 45%. Black women using hair dye every 5 to 8 weeks had a 60% higher breast cancer risk. When black-colored women applied dark-colored dyes the risk for breast cancer was 51%. When they applied light-colored dye the risk of breast cancer was 46%.
More data on hair dyes and straighteners
6. In contrast, when white women applied light-colored permanent dye, the breast cancer risk was only 12%. White women applying a dark-colored dye had a risk of 4%.
7. Hair straightener use in all women of the study was only 9.9%. Among these 74.1% of black women used them, compared to only 3% of Hispanic women. Women who used straighteners in the 12 months before enrolment subsequently developed an 18% higher breast cancer risk. Women who used straighteners every 5-8 weeks had a 31% higher breast cancer risk.
The American Cancer Society is aware that hair dyes can cause cancer. But the agency states that it is not clear what ingredients of hair dye cause cancer. Bladder cancer, leukemia, breast cancer and a few other cancers have a link to the use of permanent hair dyes. But researchers have not been able to find a causal agent that they can hold responsible for these cancers. The study here showed a strong association of the hair chemicals to the development of breast cancer. But the authors stated that they cannot conclude that this is a causation. Researchers would require a prospective and random clinical trial to answer the question of causation. However, it is unlikely that such a trial would ever be organized.
Hair dyes and straighteners may cause breast cancer. The researchers compared the statistics regarding hair dye application in white women and black women. Black women had a 45% higher breast cancer risk when they used a permanent dye for their hair. In white women there were 7% higher breast cancer rates with permanent hair dye use. The controls were white or black women who did not use hair products. Researchers found similar associations with the use of hair straighteners. Women using straighteners subsequently developed an 18% higher breast cancer risk. When women used straighteners every 5-8 weeks, they had a 31% higher breast cancer risk. But all of these data do not prove that the chemicals in hair products cause breast cancer. It only shows an association. Nevertheless, the data can utilized to minimize your danger of getting breast cancer based on the ethnic group you belong to.