A fever is a symptom, not a disease. Like all symptoms, for example cough or vomiting, a fever may be due to illnesses that are minor or serious. Fortunately, most fevers in children are due to infections that are minor and self-limiting.
Most fevers which are associated with illnesses range between 38.3°C and 40.0°C and last for 3 to 5 days. In general, the intensity of the fever does not relate to the severity of the illness. How your child behaves is what counts. Fever does not cause brain damage but may cause harm if it is more than 41.0°C. Fortunately, the brain's thermostat keeps untreated fevers below this level.
Your child must see a doctor if he or she is less than 3 months of age and has a fever.