A fever is when your body temperature rises above its normal level, usually because you're sick. Your normal temperature hovers around 98.6 degrees Fahrenheit, but when you have a fever, it might climb to 100, 101, or even higher. You feel hot to the touch, your cheeks flush red, and you might feel sweaty, achy, or exhausted.

A fever isn't actually your enemy, though it feels miserable. It's your body's way of fighting an infection. Many germs that make you sick thrive at normal body temperature but struggle when things heat up, so your body cranks up the temperature on purpose, like turning up the thermostat to make unwanted guests uncomfortable. White blood cells, which attack infections, can also work better at slightly higher temperatures.

The word fever can also describe intense excitement or enthusiasm, as when basketball fans catch playoff fever or when gold fever drove prospectors to California in 1849. This usage captures how fever makes you feel driven and consumed by something, unable to think about much else.

If you develop a high fever (above 103°F) or a fever that lasts several days, you should see a doctor or another trusted healthcare professional. Most fevers, though, break on their own once your immune system wins its battle.