Hair dye is a cosmetic for dyeing hair. Divided into temporary, semi-permanent and permanent hair dyes. Hair dyes generally contain carcinogen p-phenylenediamine. Experts say that p-phenylenediamine is a colorant that must be used in hair dyes and is an internationally recognized carcinogen. Hair dyeing has become people's fashion choice. According to a survey conducted by CCTV International, among more than 2,600 respondents, more than 90% have dyed their hair, and about half of them started dyeing their hair before the age of 30.