After a fever, a red rash may appear on the body for different reasons, due to the different physical conditions of patients and differences in the specific causes, commonly seen in the following cases: 1. measles: measles is transmitted through the respiratory tract and is common in malnourished, low-immunity, unvaccinated people, a red rash will appear on the skin on the 3rd-4th day after the fever, first appearing behind the ears, and then quickly spread throughout the body; 2. Chickenpox: Chickenpox is an acute infectious disease, commonly found in children. Chickenpox will show signs of fever at the beginning, and red rash and papules will appear on the second day after the fever, in clusters, after which the rash can evolve into a herpes; 3. rubella: rubella generally appears 1-2 days after the fever, with a rash in the form of red patches, often accompanied by swollen lymph nodes behind the ears; 4. early childhood emergency rash: for patients with early childhood emergency rash, the body temperature generally returns to normal after 3-5 days of fever, at which time there may be some Rose colored papules, lasting about 2 days the rash will subside; 5, drug allergies: allergy drugs taken at the time of fever may lead to a post-fever rash, often with itching; 6, viral rash: Echovirus, coxsackie virus and other infections cause intestinal diseases, in the fever or fever after the rash, usually 1-3 days to subside. The phenomenon of red rash after fever, it is recommended to promptly go to the hospital for examination to identify the specific reasons for the appearance of the rash after targeted treatment to strengthen drugs, daily care and other operations.