10 Things to Know

By Karla Moeller
Fever, also known as pyrexia and febrile response, is defined as having a temperature above the normal range due to an increase in the body's temperature set-point. There is not a single agreed-upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C (99.5 and 100.9 °F). The increase in set-point triggers increased muscle contractions and causes a feeling of cold. This results in greater heat production and efforts to conserve heat. When the set-point temperature returns to normal, a person feels hot, becomes flushed, and may begin to sweat. Rarely a fever may trigger a febrile seizure. This is more common in young children. Fevers do not typically go higher than 41 to 42 °C (105.8 to 107.6 °F).

Fever is a defensive response coordinated by several systems within our bodies.
Most animals have mechanisms that increase body temperature when they get infections, whether they do this physiologically or behaviorally. Some plants may also increase temperature during infection.
Organisms experiencing immune challenges often show a higher chance of survival if they have increased body temperatures.
The increased temperature itself in some cases may make bacteria and viruses grow more slowly, but the higher temperature seems to be more useful as a signal to turn on other defensive systems.
Fever is not just a result of faster metabolism, it is controlled by specialized brain centers that stabilize body temperature at a higher level. The higher body temperature during a fever is kept stable, and the body prevents it from moving either up or down.
Higher body temperatures are energetically costly in terms of calories expended, about an extra 10 to 12.5% increase in metabolic rate per degree fever centigrade.
Blocking fever sometimes makes it harder to fight infections, but the body has many other mechanisms to fight infection so sometimes blocking fever can be safe.
Groups of scientists and doctors have steadily changed recommendations about fever in recent decades to reduce the use of drugs to reduce fever.
Epileptic seizures associated with fevers in children are usually not a direct result of the high temperature itself but of the infection.
Some children who take aspirin for fever can develop Reye syndrome.