Many rashes have their own crossovers, and sometimes it is difficult for a professional dermatologist to diagnose it. In addition, some severe rash diseases, if not diagnosed and differential diagnosis, will delay the treatment of the disease and affect the prognosis. Different diseases and rash morphological characteristics have the same characteristics, so the diagnosis of diseases needs to be considered in combination with medical history, and there are many rash diseases treated differently. Why do we need to recognize which kind of disease? In order to judge the prognosis! Can not over-treatment, can not let go of heavy patients, be alert to severe cases!!!