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 98.6°F (37°C) orally. It can change during the day from a low of 97.4°F (36.3°C) in the morning to a high of 99.6°F (37.6°C) in the late afternoon. Mild elevations—(99.8°F (37.7°C)— 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 100.4°F (38°C) or higher measured rectally.