A fever isn't an illness itself, but it's usually a sign that something out of the ordinary is going on in your body. Fevers aren't necessarily bad. In fact, fevers seem to play a key role in helping your body fight off a number of infections.

If you're an adult, a fever may be uncomfortable, but it usually isn't dangerous unless it measures 103 F or higher. For very young children and infants, however, even slightly elevated temperatures may indicate a serious infection.

Because a fever can occur with many different conditions, other signs and symptoms can often help identify the cause.

Most fevers go away in a relatively short time — usually within a few days. Not all fevers need treatment with medications. And it's possible for fever medications to have side effects, especially for the very young.