Erythema is a rash or maculopapular rash of reddened skin that has a variety of causes. Treatment is based on the manifestations and symptoms of the lesions. Common diseases include urticaria, chickenpox, and measles. Urticaria, in turn, is divided into allergic urticaria and papular urticaria. Allergic urticaria is a red, wind-like lesion on the skin caused by the body’s allergy to a substance, which is scattered and partially fused into patches with itching. It is often acute and can heal spontaneously after a few hours, but oral anti-allergy medication may also be used. Papular urticaria is mainly a red papule with intense itching caused by allergy to mosquitoes and insects, which can be controlled by oral anti-allergy medication to suppress itching plus topical glucocorticoid ointment. Chickenpox is an infection of varicella zoster virus causing skin lesions, manifested as a maculopapular rash on the head, face and extremities, with blisters in the center of the papule, surrounded by a red halo, accompanied by chills and low fever. Treatment is with antiviral medication and early antibiotics to prevent infection if there are complications. Measles is a highly contagious viral disease caused by the measles virus, manifesting as a dense rose or dark red papular rash with fever behind the ears, hairline, face, trunk and extremities. For treatment, prompt hospital consultation, appropriate investigations, symptomatic supportive treatment in principle, and active prevention of complications are given. If a rash appears clinically, you should go to the hospital promptly, cooperate with the examination according to the advice given by the specialist, and actively treat it to facilitate early recovery.