Is it true that hair dye causes cancer? 

Many studies have been conducted both domestically and internationally on the safety of hair dyes.
The British Medical Journal published a large prospective study in 20 years, which had more than 120,000 participants over a period of 36 years, and eventually found that the use of permanent hair dyes may increase the risk of skin cancer, breast cancer, ovarian cancer, and lymphoma.
The National Institutes of Health similarly found that women who used permanent hair dye within 1 year were 9% more likely to develop breast cancer than women who never used hair dye.
A team from the U.S. National Cancer Institute also studied the risk of hair coloring in men by analyzing 28 years of data from nearly 30,000 Finnish men and found that permanent hair dyes were positively associated with prostate cancer in men, with a significant 77% increase in the risk of prostate cancer.
Liu Wei, director of the Dermatology Hospital of the Air Force General Hospital, said that hair dyes may damage the body because of the chemical components they contain, especially benzodiamines. This substance is allergenic on the one hand, and on the other hand, animal experiments have found that it may cause genetic mutations and cause cancer.