It's a familiar situation: your child complains that she's not feeling well. You put your hand on her forehead and realize that she's hot. Now what? To help understand how to take her temperature accurately and how to measure a fever, read our children's fever guide.

What is a fever? A fever is an elevated body temperature. It's a symptom, not an illness. “Similar to vomiting or diarrhea, it's a flag that something is not right in the body,” explains Dr. Tom Metcalf, a pediatrician at Willowcreek Pediatrics in Salt Lake City , Utah , and father of three grown children.

A fever is not always caused by a serious illness. True, it can be a sign of a bacterial infection (meningitis, pneumonia, whooping cough, for example), but that happens less often these days due to immunization. More often it's a sign of a viral infection (cold, flu, for example), the result of a medication overdose, or even overheating from overdressing.

Also, it's not necessarily something to fear. “A fever can actually be your child's friend,” says Dr. Metcalf. It fights infection because bacteria and viruses don't grow well in high temperatures and it also increases the child's immune response because antibodies and white blood cells work better in higher temperatures.