Hair dye contains certain carcinogenic ingredients, there is no exact data on how many times a year hair dyeing causes cancer, but it is recommended to try to control it within 2 times a year. Almost all synthetic hair dyes have p-aniline, diamine compounds, and mustard amine compounds in them, all of which have carcinogenic effects. If hair is dyed too often, cancer may occur if too many carcinogenic ingredients are absorbed into the body. Temporary hair dye, the particles are larger just deposited on the surface of the hair, the interaction with the hair is not strong, and can be dyed 2 times a year. Semi-permanent or permanent hair coloring is recommended not to exceed 1 time a year. It is important to note that the composition of the hair dye must be clear before dyeing, it is best to choose a pure plant hair dye, and the scalp should not be broken when dyeing to prevent infection. If contact dermatitis occurs after hair dyeing, you must seek medical attention and avoid using similar hair dye products again.