In February 2018 researchers from the UK published their review of the medical scientific literature to assess the use of hair dyes and the risk of breast cancer. A total of 8 studies were included in the review. Results showed that there appeared to be an 18.8% increased risk of future development of breast cancer among hair dye users.
Gera R et al. Does the Use of Hair Dyes Increase the Risk of Developing Breast Cancer? A Meta-analysis and Review of the Literature. Anticancer Res. 2018 Feb;38(2):707-716