Formerly also known as lichen planus and commonly known as sweat patches, this disease is caused by Malassezia infection, and is also affected by genetic factors, environmental factors, the patient’s physical condition, the immune system and other factors. Malassezia belongs to the conditionally pathogenic bacteria, in the appropriate conditions can violate the skin stratum corneum and thus cause the disease. 1. Genetic factors: this disease has a certain genetic susceptibility, family history of disease risk increases. 2. Environmental factors: high temperature and humid environment is easy to get sick, in the southern tropical and subtropical areas and high temperature and humid environment. 3. Patient’s constitution: excessive secretion of skin oil or sweating. 4. Immune system: such as long-term application of glucocorticoids and immune agents. In order to further clarify the cause of the disease, should go to the hospital in time.