Alopecia areata is the phenomenon of hair loss. Normal hair loss is the hair in the regressive and resting phases. It is possible to 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, and has many causes. 1. Androgenetic alopecia: It is an autosomal dominant genetic trait, and its genetic characteristics need to be manifested only under the action of androgens. 2. Neurogenic alopecia: hair loss often increases when mental stress is excessive. Under the effect of mental stress, the human body hair standing 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. 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, and severe malnutrition even leads to diffuse alopecia. 5. Physical alopecia: The 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: Infection by various pathogens is 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 alopecia: developmental defects caused by the complete absence or thinning of hair, patients commonly thin and fine hair, or normal hair at birth, soon after shedding without regeneration, can be divided into isolated defects and other deformities. 10. Seasonal hair loss: generally easy to lose hair in summer, because the high temperature of summer pore expansion leads to hair loss, not easy to lose hair in autumn and winter, because the temperature drops in this period pore closure Chemotherapy drugs have a powerful killing power to cancer cells, but so far, any chemotherapy drugs can not selectively kill only cancer cells, while killing cancer cells will also damage the body’s normal cells. The normal hematopoietic cells, mucous membrane cells of the digestive tract and hair follicle cells, which are actively proliferating in the body, are more vulnerable to damage. Damage to hair follicle cells, which are responsible for hair growth, can cause hair loss. Hair loss can occur anywhere on the body, including the head, face, underarms and pubic area. During chemotherapy, hair usually does not fall out immediately, but often occurs 2-3 weeks after the start of chemotherapy. After a period of chemotherapy, the hair falls out gradually or in clumps, and the remaining hair becomes dry and lusterless. The drugs that most long cause hair loss are etoposide, paclitaxel village, adriamycin, cyclophosphamide, etc. The degree of hair loss due to chemotherapy drugs is not only related to the type of drug, but also to the dose of the drug. In addition, the degree of hair loss is not uniform from patient to patient, and the effect of different regimens on hair loss varies greatly. Patients do not need to worry too much about the “spring breeze”. It is understood that hair loss caused by chemotherapy is generally reversible, 1-2 months after stopping the drug hair regeneration, and often darker, thicker and more shiny than before.