Hair dyes are cosmetics that belong to the hair coloring category. Started in the late 19th century, modern hair dyes are developed on the basis of the organic substance “”p-phenylenediamine””. According to the dye is divided into vegetable, mineral, synthetic hair dyes; 1. According to the degree of dyeing firmness is divided into temporary, semi-permanent category, permanent category. Hair dyes use p-phenylenediamine, resorcinol, have a certain degree of toxicity, some reports of carcinogenicity of these ingredients. In the process of hair coloring, the hair dye touches the scalp or the skin in the area of hair coloring, penetrates into the surface layer of the skin, and can produce skin irritation, therefore, prolonged hair coloring has skin toxicity and carcinogenicity. 2, for the plant hair dye, just the difference between the dye composition, for the use of hair dye fixing agent and penetrating agent in fact, there is no great difference. That is to say that plant hair dye is not so safe and secure as advertised. For long-term hair coloring people, can only be the use of hair dye as little as possible to contact the skin, reduce the skin absorption of hair dye method, which is very important. 3, you can try not to wash your hair before the use of hair dye, because the oil on the surface of the skin has the effect of blocking the penetration of hair dye into the skin. 4, when dyeing hair as little as possible with hair dye, just dyeing the new growth of hair can be, reduce the use of dose and frequency, can to a certain extent reduce the contact time with the skin, reduce skin absorption. Hair coloring frequency as far as possible to control in the year 4 times below is better.