Hair loss is a relatively common disease, because of the impact of beauty, patients are eager to seek medical treatment, but the causes of hair loss are more, the diagnosis is often based on clinical symptoms. The following is an introduction to common diseases: 1, androgenetic alopecia: mainly seen in men aged 20-30 years, from the forehead on both sides of the hair density decline, the formation of “high forehead, serious only occipital and two temporal residual hair. Women mostly show thinning hair on the top of the head, generally not involving the temporal frontal area. This disease should be distinguished from secondary alopecia such as malnutrition, drugs, endocrine diseases and iron deficiency anemia. If female patients have severe acne, hirsutism, and masculinization should first be excluded from endocrine disorders. 2. Alopecia areata: occurs at any age, with sudden, limited hair loss, normal local skin and no conscious symptoms. 30%-50% of patients have new hair growth within 6-12 months. However, individual differences are large, and 2/3 patients recover only after 5 years. The more extensive the hair loss, the greater the chance of hair re-shedding and the high recurrence rate. 3.Growth phase hair loss: caused by cytotoxic drugs, vitamin A, Prenalol, thiouracil, etc., and recovered after stopping the drugs. 4, resting hair loss: postpartum, discontinuation of birth control pills, high fever, malnutrition, anemia, surgery, serious mental factors lead to.