Normal body temperature may change during any given day. It is usually highest in the evening. Other factors that may affect body temperature are:

A woman's menstrual cycle. In the second part of this cycle, her temperature may go up by 1 degree or more.

Physical activity, strong emotion, eating, heavy clothing, medicines, high room temperature, and high humidity can all increase body temperature.

Fever is an important part of the body's defense against infection. Most bacteria and viruses that cause infections in people thrive best at 98.6°F (37°C). Many infants and children develop high fevers with mild viral illnesses. Although a fever signals that a battle might be going on in the body, the fever is fighting for, not against the person.

Brain damage from a fever generally will not occur unless the fever is over 107.6°F (42°C). Untreated fevers caused by infection will seldom go over 105°F (40.6°C) unless the child is overdressed or in a hot place.

Febrile seizures do occur in some children. Most febrile seizures are over quickly and do not mean your child has epilepsy. These seizures also do not cause any permanent harm.

Unexplained fevers that continue for days or weeks are called fevers of undetermined origin (FUO).