You've had the feeling before — you come home from school feeling awful with a sore throat. Your mom feels your head with her hand, frowns, and takes your temperature with a thermometer. Within a few minutes, you hear the word fever.

But what are fevers, exactly? Why do kids get them? Why do parents and doctors care so much about them? And once you have one, how do you get rid of it? Don't go back under the covers just yet — read on to learn more about the facts on fever.

It All Begins in Your Brain

To really understand what a fever is, you need to say hello to the hypothalamus (say: high-po-thal-uh-mus). The hypothalamus is in the center of your brain. Think of it as your body's thermostat — like that thing on the wall in your house that you use to set the heat or the air conditioning. Your hypothalamus knows what temperature your body should be and will send messages to your body to keep it that way.

Most human beings have a body temperature of around 98.6° F (37° C). Some people will have a normal temperature that's a little higher; others will have a normal temperature that's a little lower.

Most people's body temperatures even change a little bit during the course of the day: It is usually a little lower in the morning and a little higher in the evening. For most kids, their body temperature stays pretty much the same from day to day — until germs enter the picture.

The Germs March In

Remember that strep throat that made you feel so rotten? Or another time when the flu made you feel tired and achy? These kinds of infections are caused by germs that make their way into your body, usually in the form of bacteria (say: bak-teer-ee-uh) or viruses.

Once these germs march in and make you sick, they can sometimes cause certain chemicals to flow into your blood. When your hypothalamus gets word that these chemicals are on the scene, it automatically sets your body's thermostat higher. Instead of saying your body should be 98.6° F (37° C), your body's thermostat might say that it should be 102° F (38.9° C).

Why does the hypothalamus tell your body to change to a new temperature? Researchers believe turning up the heat is the body's way of fighting the germs and making your body a less comfortable place for them. A fever is also a good signal to you, your parents, and your doctor that you are sick. Without fever, it's much more difficult to tell if a person has an infection. That's why grown-ups are concerned when you have a fever.

Shiver, Then Sweat

Once your hypothalamus sets a new temperature for your body, your body takes action and starts to heat up. When a fever starts, your body gets hotter and you may shiver without thinking about it to create more heat. You may feel very cold even though the room isn't cold and even though you have your pajamas or nightgown on and lots of blankets around you.

If your body reaches the new temperature that's been set by the hypothalamus — say 102° F (38.9° C) — you won't feel cold anymore. According to your hypothalamus, your temperature is where it should be!

After the cause of the fever disappears, your hypothalamus will set everything back to a normal temperature. When your strep throat medicine starts to work, for instance, your body will begin to cool down. You'll begin to feel warm and will need to get rid of the extra heat that's been in your body. You may sweat and decide to change into some lighter-weight pajamas.

Fighting a Fever

For almost all kids, fevers aren't a big problem. Once the cause of the fever is treated or goes away on its own, your body temperature comes back down to normal and you feel like your old self again. Most doctors agree that many kids with a fever don't need to take any special medication unless their fevers are making them uncomfortable.

It's a different story for newborns and very young infants, though. They should be evaluated by a doctor for any fever that reaches 100.4° F (38° C) or higher.

If a kid has a higher fever and feels uncomfortable, the doctor might tell a parent to give the child medicine. The two medicines most often recommended are acetaminophen (say: uh-see-tuh-min-uh-fen) or ibuprofen (say: eye-byoo-pro-fen). The medicine blocks the chemicals that tell the hypothalamus to turn up the heat. Kids should never take aspirin to treat a fever because it can cause a rare but serious illness.

If you have a fever, your mom or dad will probably ask you to drink more fluids than usual. That's important because as your body heats up, it's easy for it to get dehydrated (say: dee-hi-drayt-ed), which means there isn't enough water in your body. You have a lot of choices when it comes to fluids — juice, water, sports drinks, soup, flavored gelatin, and even ice pops.

Before you know it, your mom or dad will pull the thermometer out of your mouth and say, "Your temperature is normal. No more fever!"

Reviewed by: Kate M. Cronan, MD
Date reviewed: September 2010