1, genetic factors: genetic factors account for a large proportion. If one parent has more hair, the child will have more hair;

2, skin condition: if the skin is white, it will appear hairy, and if the skin color is deep, the hair will appear less;

3. The role of androgen: Both boys and girls will have androgen secretion. If hair follicles are sensitive to androgen, the same dose of androgen may lead to increased hair. If the hair follicle is not sensitive, there will be less hair. In addition, after men enter puberty, the secretion of androgen will increase and the hair will increase;

4, drug effect: if children take a drug, it will also cause an increase in hair;

5. Disease factors: trichomoniasis, congenital diseases and endocrine diseases, for example, will cause hair growth, which needs to be comprehensively judged in combination with the clinical symptoms of the whole body.