If the baby has a red rash all over the body after a fever, the specific reasons are as follows: a. If the rash is caused by allergic factors, the child will be accompanied by itching symptoms, can give oral desensitizing drugs, such as loratadine, with vitamin C for oral intake, can effectively relieve the symptoms of allergy. The rash is a hemorrhagic rash because the baby’s immune function decreases after a fever, which may be thrombocytopenic purpura, mild cases can continue to give symptomatic treatment, serious cases need to go to the hospital for platelet-raising medication. If the red rash appears after the fever has subsided, it is considered to be a viral rash, which does not need to be treated, and only for the child’s symptoms, the recovery period continues to take oral medication to consolidate treatment, while avoiding oral hair products, fish, shrimp, eggs, beef and mutton do not eat, do not take a bath for three days, do not see the wind, that can make the rash disappear.