Frequent shampooing and dandruff are, firstly, commonly caused by physiological factors, and many people wash their hair too frequently because they do not want to have dandruff to affect their appearance, which damages the scalp cuticle and not only does not reduce dandruff production, but also promotes dandruff production; secondly, it may also be caused by pathological factors, such as seborrheic dermatitis, Malassezia infection, psoriasis, etc.: I. Physiological factors 1. Inappropriate shampooing methods. Frequent shampooing, unsuitable shampoo, too high water temperature, or scratching the scalp with nails and pulling hair loss will damage the scalp and hair oil, stimulate the keratinization of scalp epithelial cells and produce dandruff; 2. Lack of sleep: it will increase the amount of scalp oil secretion, affect the normal blood circulation, hinder the absorption of nutrients by hair follicle cells, and lead to an increase in dandruff. Second, pathological factors 1, seborrheic dermatitis: it will not only produce a large amount of dandruff, but also have symptoms such as greasy scalp, itchiness and pain, and finally cause serious hair loss problems; 2, Malassezia infection: some studies believe that dandruff production is related to the overproliferation of fungi, among which the study of Malassezia infection is the most common, and Malassezia lipolytic enzyme can produce free triglycerides in sebum by hydrolyzing fatty acids, which stimulates an inflammatory response in the skin. Clinical manifestations may be head oil, itching, increased dandruff, etc., which may also cause hair loss, etc.; 3. Psoriasis: the head is a very good site for psoriasis, with patchy lesion symptoms visible between hair traces, mainly manifested as erythematous patches covered with thick scales, sometimes fused into patches, which may produce more scales.