A lot of red rashes on the body after a fever may be an infectious rash or a drug rash caused by medication. Fever and rash can occur in many infectious diseases, such as measles, rubella, rubella, chickenpox. Most rashes begin to appear 2-3 days after the onset of fever, and infantile rashes usually appear after the fever subsides. Various infectious rashes have their own rash characteristics and rash patterns, and require medical attention to determine the type of infection based on the symptoms and examination, and to provide appropriate antiviral and supportive treatment. Drug-induced rash should be considered if a large, fixed rash or a polymorphic, generalized, symmetrical rash with blisters develops after the use of antipyretics or other medications during a fever. The cause of the disease is related to the patient’s allergy, the treatment needs to immediately stop using drugs that may cause allergic reactions, and according to the severity of the disease, follow the doctor’s instructions to use antihistamines or glucocorticoid shock therapy to improve the symptoms and alleviate the disease.