The causes of hair loss include physiological factors and pathological factors (common in baldness, androgenetic alopecia, alopecia areata and other diseases). 1. Physiological factors: generally normal people will lose hair, regardless of health and work and rest, different groups of people have more or less hair loss phenomenon, but the daily hair loss of less than 100, are normal phenomena, but if the daily hair loss of more than 100, is due to pathological factors. 2. Pathological factors (1) Patchy baldness: the etiology of this disease is unknown, may be related to genetic, mental and emotional stress, endocrine disorders, immune inflammation and other factors, may belong to the category of polygenic diseases, genetic susceptibility is an important factor in the development of patchy baldness. (2) Androgenetic alopecia: this disease has a genetic predisposition, 5α-dihydrotestosterone and androgen receptor binding on hair follicle cells, play a biological role, making the hair follicle miniaturization, anagen hair gradually thinning, hair growth cycle shortening, so that the original coarse black hair gradually become light-colored hair, and ultimately, the hair follicle atrophy, hair shedding. (3) Resting hair loss:This disease can be caused by endocrine factors, such as hypothyroidism, postpartum or after the withdrawal of contraceptive pills; nutritional factors, such as calories, protein, essential fatty acids, etc. intake is too low; drug factors, such as antidepressants, angiotensinase converting agents, etc., which lead to excessive loss of normal resting pestle hair. It is recommended that patients, if they suspect that the disease is caused by the disease, go to a regular hospital, a clear diagnosis, for treatment, to avoid delay.