Fever is a symptom, not an illness. When an infection occurs, the immune system will launch an attack to try to remove the cause. A high body temperature is a normal part of this reaction.
Fever will usually resolve on its own. However, if body temperature rises too high, it may be a symptom of a severe infection that needs medical treatment. Mild fever is part of the immune system’s response to bacteria, viruses, and other pathogens. It helps the body fight off infection. Core body temperature varies from person to person. Most experts consider a temperature of 100.4° F (38°C) to be a fever, but in children, this may be lower, at 99.5°F (37.5°C).