The causes of cuirass include genetic factors, endocrine factors, food and drug factors, certain diseases and so on. Cuii hair is the body surface white soft and thin hair, because there is no medulla and more than other hairs. The common reasons for the increase of cui hair are as follows. 1. Hereditary factors: If the parents have heavy cui-ui hair, then their children have a greater chance of cui-ui hair. 2. Endocrine factors: skin follicles are sensitive to male hormones, abnormal hormone levels in the body can also lead to the production of fine animal hair. 3. Food and drug factors: if the patient took prednisone, cortisone, testosterone and other drugs or ate too much hormone-containing food, then these hormones can stimulate the body to grow a lot of fine hair. 4. Certain diseases: such as adrenal tumors will make glucocorticoid abnormal increase, polycystic ovary syndrome will make sex hormone levels abnormal, these diseases will lead to increase in cui hair. Finally, the phenomenon of abnormal increase of cui hair, please go to the regular medical institutions in time, clear cause of the symptomatic treatment.