Fever is an increase in body temperature that can be a symptom of an underlying illness in a child. It is not an illness in itself, except in the case of heat stroke. Fever is the body’s response to disease and is designed to kill germs outright and stimulate the immune system to fight bacteria and viruses.

Fever may develop at various speeds and may reach heights ranging from 100.4 degrees to 104 degrees Fahrenheit (38 degrees and 40 degrees Celsius) or higher. Fevers are either acute (short duration with a definite endpoint) or chronic (recurring repeatedly over time). Because fever is a natural and healthy response to illness, it typically does not need to be treated except to relieve a child’s discomfort. A thermometer can be used to detect a fever. These instruments come in many varieties.

Children who have a fever are likely to experience associated symptoms such as perspiration, flushed appearance, lethargy or fatigue, loss of appetite (anorexia), chills, muscle aches and headaches. A febrile seizure may occur in children with very high fevers and is marked by temporary loss of consciousness and convulsions. Very high fevers also can cause hallucinations, confusion and irritability.

Viral and bacterial infections are the source of most acute fevers, while a number of medical conditions – including juvenile rheumatoid arthritis, chronic or relapsing infections and cancer – can cause chronic fevers. In rare cases, no cause can be determined for a persistent fever. Such conditions are described as “fevers of unknown origin.”

Fever itself is generally not an illness and usually does not require treatment. Nonetheless, parents often desire to reduce a fever because of the discomfort it may cause to a child. Non-aspirin fever reducers can be used to reduce a fever and lessen associated symptoms such as achiness and chills. Children also should get plenty of rest and drink plenty of fluids to avoid dehydration. Other techniques that may be useful in keeping children comfortable include dressing the child in light clothing and cooling the child with lukewarm sponge baths.

Parents are urged to consult a physician when a child under 6 months of age has a fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or a child older than 6 months has a fever of 101 degrees Fahrenheit (38.3 degrees Celsius) or higher. Any fever in an infant who is 3 months old or younger always should be reported to a healthcare professional, preferably a pediatrician, because it often indicates a potentially serious infection. Parents should also take their child to a physician if the fever is accompanied by various other symptoms (e.g., rash, seizure).

Though fevers cannot always be prevented, frequent handwashing can help prevent children from picking up germs and infecting themselves by touching their mouths, nose or eyes.