Normal hair loss is all hair in the regressive and resting phases, which can maintain a normal amount of hair because the hair entering the regressive phase and the new hair entering the anagen phase are constantly in dynamic balance. Pathological hair loss refers to abnormal or excessive hair loss, which has many causes. 1, androgenetic alopecia is an autosomal dominant genetic inheritance, and its genetic characteristics need to be manifested only under the action of androgens. 2, neurogenic alopecia Hair loss often increases when there is excessive mental stress. Under the effect of mental stress, the human body hair muscle contraction, hair erection, plant nerve or central nervous function disorder, hair follicle papilla change and malnutrition, resulting in hair growth function inhibition, hair into the resting phase and hair loss. 3, endocrine alopecia Hair growth is affected by a variety of endocrine hormones, so when endocrine abnormalities occur more hair loss diseases, such as postpartum, menopausal hair loss. 4, nutritional alopecia Hair is the external manifestation of the body condition, malnutrition and metabolic abnormalities of the body can cause changes in hair quality and hair color, severe malnutrition and even lead to diffuse hair loss. 5, physical hair loss Common physical factors that cause hair loss include mechanical stimulation and exposure to radioactive substances. 6, chemical alopecia Chemical factors can lead to hair color change or even hair loss. 7.Infectious alopecia Various pathogenic infections are an important factor in hair diseases, mainly including bacterial, viral, fungal, helminthic, parasitic and other infections. 8, symptomatic alopecia Certain systemic or local diseases can be accompanied by hair loss. 9, congenital hair loss Developmental defects caused by the complete absence or thinning of hair, patients commonly thin and fine hair, or normal hair at birth, soon after the loss of non-regeneration, can be divided into isolated defects and other deformities. 10, seasonal alopecia Generally easy to lose hair in summer, because the high temperature of summer pores expansion led to hair loss, autumn and winter is not easy to lose hair, because the temperature of this period fell pores closed.