A red rash on the body after a fever is common in pediatric patients who have an acute rash in young children. It is a common acute febrile rash in infants and young children, which is characterized by the appearance of rose-red papules on the skin as the fever subsides. In addition, it is also common in some blood diseases, such as acute leukemia and idiopathic thrombocytopenic purpura. For patients with early childhood acute rash, after 3 to 5 days of fever, the body temperature returns to normal and some rose-colored maculopapular rash may appear at this time, which lasts for about two days and the rash will subside without leaving any trace. If the child was healthy in the past, no special treatment is needed, and symptomatic antipyretic drugs can be used for high fever. If the patient has hepatosplenomegaly, emaciation, weakness, or even bleeding from the skin and mucous membranes, hematological disease is considered, and this condition needs to be treated by a specialized discipline. Patients with a red rash on the body after a fever, along with a history of drug use, need to consider drug allergies caused by, for example, cold medicine or antibiotics, drugs produce allergic symptoms, the body may have a red rash after taking the drug, the rash is in the form of a wind rash, red in color, accompanied by itching symptoms, need to stop using the suspected allergy drugs, or oral paracetamol. Viral infections can also cause a red rash, most of which is non-specific and has a variety of forms, and the rash will usually clear up automatically within a day or two after the fever has cleared up, so no special treatment is needed. The red rash that appears on the body when you have a fever can be mild or severe. In addition to common viral infectious diseases such as toddler rash, hand, foot and mouth disease, chicken pox, rubella and measles, there are also some blood diseases and other diseases that can have similar symptoms.