Rash after fever may be due to drug rash, or scarlet fever, measles and other diseases. 1. Drug rash: the body’s resistance decreases during fever, and if you have used antipyretic and analgesic drugs such as aspirin and acetaminophen before, it may cause drug rash, and the patient’s skin will have a red rash, which is a manifestation of the adverse reaction to drugs. 2. Scarlet fever: the disease is caused by group A beta-hemolytic streptococcus, which can be transmitted through air droplets, and in a few cases, it may also be transmitted through close contact or skin trauma. Clinical symptoms are mainly characterized by a red rash that begins the day after the onset of fever. 3. Measles: the pathogen of this disease is measles virus, mainly through the respiratory tract for droplet transmission, common symptoms include fever, cough, runny nose, red eyes, etc., most patients with fever for about three days will begin to appear red rash. There are more reasons for the red rash after fever, patients need to go to the hospital to clarify the specific cause.