The rash on the body in clinical dermatology is a very common skin manifestation, can cause a rash on the body for many reasons, in daily life the most common are mainly the following causes: 1, allergic dermatitis: if the patient eats some food, exposure to pollen, dust, chemicals, easily cause hypersensitivity reactions, there will be a generalized papular rash, and accompanied by severe itching. 2, solar dermatitis: after prolonged exposure to ultraviolet light, there will be an inflammatory skin reaction, and accompanied by a sense of pain or itching: After prolonged exposure to ultraviolet light, there will be an inflammatory reaction of the skin, manifested in the appearance of corn papules of rice-grain size on the body, and accompanied by a sense of pain or itching. 3, Phase II syphilis rash: Patients infected with syphilis through adverse sexual contact will develop a generalized rash, also known as syphilis rash, during Phase II syphilis. 4, nodular itchy rash: Due to damage to the immune system, the skin will also appear red spots papular rash.