Fever is the body's normal response to infection and other conditions, both minor and serious. Most fevers help the body fight infection.

The average normal body temperature is about 37°C (98.6°F). It usually rises during the day from a low of 36.5°C (97.7°F) in the morning to a high of 37.5°C (99.5°F) in the late afternoon. Mild elevations—[37.7°C (99.8°F)]— can be caused by too much clothing, a hot bath, or hot weather.

Fever in a child is present when a child's temperature is 38°C (100.4°F) or higher measured rectally.