Fevers

What Is a Fever?

Fever happens when the body’s internal “thermostat” raises the body temperature above its normal level. This thermostat is found in a part of the brain called the hypothalamus. The hypothalamus knows what temperature your body should be (usually around 98.6°F/37°C) and will send messages to your body to keep it that way.

Most people’s body temperatures even change a little bit during the course of the day: It’s usually a little lower in the morning and a little higher in the evening and can vary as kids run around, play, and exercise.

Sometimes, though, the hypothalamus will “reset” the body to a higher temperature in response to an infection, illness, or some other cause. Why? Researchers believe that turning up the heat is a way for the body to fight the germs that cause infections, making it a less comfortable place for them.

What Causes Fevers?

It’s important to remember that fever by itself is not an illness — it’s usually a symptom of another problem.

Fevers can be caused by a few things, including:

Infection: Most fevers are caused by infection or other illness. A fever helps the body fight infections by stimulating natural defense mechanisms.

Overdressing: Infants, especially newborns, may get fevers if they’re overbundled or in a hot environment because they don’t regulate their body temperature as well as older kids. But because fevers in newborns can indicate a serious infection, even infants who are overdressed must be checked by a doctor if they have a fever.

Immunizations: Babies and kids sometimes get a low-grade fever after getting vaccinated.

Although teething may cause a slight rise in body temperature, it’s probably not the cause if a child’s temperature is higher than 100°F (37.8°C).

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