Topic Overview

Fever is the body's normal and healthy reaction to infection and other illnesses, both minor and serious. Most fevers help the body fight infection. Fever is a symptom, not a disease. In most cases, fever means your child has a minor illness. Often you must look at your child's other symptoms to determine how serious the illness is. Most infections with a fever are caused by viruses.

The average normal body temperature is 98.6°F (37°C) orally. It usually changes during the day from a low of 97.4°F (36.33°C) in the morning to a high of 99.6°F (37.56°C) in the late afternoon. Every individual child has a normal temperature range that may be different from any other child. Mild increases [100.4°F (38°C)] can be caused by wearing too many clothes, taking a hot bath, or being out in hot weather.

A child has a fever when his or her temperature is 100.4°F (38°C) or higher, measured rectally. Rectal temperatures are the most accurate for checking a fever in a young child. Oral temperatures read about 1° F (.5° C) lower than rectal temperatures. All temperature guidelines listed in this topic are rectal. Other ways to measure temperature, such as ear probe thermometers, forehead temperature strips, or pacifier thermometers, may not be as reliable or accurate. For information about taking accurate temperatures in infants and children, see the topic Body Temperature.

Most children with a fever will be fussy, play less, and may not eat as much as usual. High fevers are not comfortable, but they rarely cause serious problems.

In children, fevers can be caused by viral infections such as colds, flu, and chickenpox. It is not unusual for a preschool-aged child to have 7 to 10 viral infections in a year. Each new viral infection may cause a fever. It may seem that a fever is ongoing, but if 48 hours passes between fevers, then the new fever is most likely from a new illness. Fevers can occur after immunizations. Teething does not cause a fever. If a baby is teething and has a fever, other symptoms may be present and need to be evaluated.

The degree of fever may not indicate how serious the illness is. With a minor illness, such as a cold, a child may have a temperature of 104°F (40°C). A very serious infection may cause little or no fever. It is important to look for other symptoms along with the fever. A fever without other symptoms that lasts 3 to 4 days, comes and goes, and gradually reduces over time is usually not a cause for concern.

Children tend to run higher fevers than adults. There is no medical evidence that fevers from infection can cause brain damage. The body limits a fever caused by infection from going above 106°F (41.11°C). However, when the body's temperature goes up because of heat—such as from being in a car parked in the sun—the temperature of the body can go above 107°F (41.67°C)and brain damage can occur.

A fever that increases quickly may lead to a febrile seizure in some children. If a seizure occurs, see the topic Fever Seizures in Related Information.