You're drenched in sweat. Your head is filled with a dull, throbbing ache, and, worse, you feel like someone is pressing their thumbs against your eyelids. One minute you feel afire; the next minute you are overcome with shaking chills. You put a thermometer under your tongue, and the mercury climbs to 101 degrees Fahrenheit. Yep, you have a fever.
To understand what having a fever means, and what you should or shouldn't do about it, it helps to know something about how the body controls temperature. There is quite a range in what is considered normal in body temperature. (By the way, everyone has a temperature; when it rises above what is considered normal and stays there, it is termed a fever. ) The body's natural temperature-control system, located in a tiny structure at the base of the brain called the hypothalamus, is normally set somewhere around 98.6 degrees Fahrenheit. A normal temperature measured orally ranges from 96.7 to 99.0 degrees Fahrenheit (taken rectally, it measures one degree Fahrenheit higher). Your own temperature probably varies by more than two degrees during the course of a day, with the lowest reading usually occurring in the early morning and the highest in the evening.
Fever is not a disease in itself but a symptom of some other condition, usually an infection caused by bacteria, fungi, a virus, or parasites or even an allergic reaction. When this enemy invades, white blood cells are triggered to attack, releasing a protein called endogenous pyrogen. When endogenous pyrogen reaches the brain, it signals the hypothalamus to set itself at a higher point; if that new set point is over 100 degrees Fahrenheit, you have a fever.
When that happens, what should you do? Here's some advice:

Let it be.
The fact is, fever may do the body son good. An untreated fever tends to be self limited relatively benign, and contrary to popular belief not likely to escalate to the point that it causes harm. Nor does lowering fever mean that you are lessening the severity of the illness; indeed fever may be the body's way of mobilizing itself against invading organisms. Over more than a decade of research, studies show that elevated body temperatures can enhance the immune response, says Matthew J. Kluger, Ph.D., professor of physiology at the University of Michigan Medical School in Ann Arbor. This heightened immune response is brought about by pyrogen, the same protein that causes the hypothalamus to reset itself. And pyrogen also has the ability to withhold iron from the blood, which apparently keeps infectious organisms from feasting and flourishing. By leaving a fever untreated, you may be following Mother Nature s way of dealing with infection, says Kluger. There are, however, some noteworthy exceptions to this let it be approach (see Hello, Doctor? for more information on when to call the doctor). In addition, if you are feeling truly miserable, there are some steps you can try to make yourself more comfortable when you have a fever.

Dress comfortably.
Let your body tell you what to wear. If, as the fever is developing, you get the chills, bundle up until you feel more comfortable. On the other hand, if you feel uncomfortably warm, shed some clothing. With your body exposed as much as possible, your sweat glands will be better able to release moisture, which will make you feel more comfortable. The fewer the clothes, the faster the fever will go down, says Pascal James Imperato, M.D., professor and chairman of the Department of Preventive Medicine and Community Health at State University of New York Health Science Center at Brooklyn. Avoid overbundling an infant.

Don't go under cover.
Unless you have the chills, bundling yourself in bed under a pile of blankets or quilts will only hold the heat in and make you more uncomfortable. Forget everything you've heard about sweating the fever out by piling on the covers, advises Harold Neu, M.D., professor of medicine and pharmacology at Columbia.
University College of Physicians and Surgeons in New York. Once again, let your body be your guide. If a light sheet makes you feel more comfortable, don't feel that you have to bury yourself under blankets.

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Sip.
Fever, especially if it is accompanied by vomiting or diarrhea, can lead to fluid loss and an electrolyte imbalance. Keep yourself well hydrated, says Neu. Cool water is best, but unsweetened juices are OK if that's what tastes good. Getting a child to drink plenty of water is sometimes difficult; try Popsicles or flavored ices, which are primarily water.

Don't force food down.
Don't force yourself to eat if you don't feel like it when you have a fever, says Imperato. Your body will tell you when it's time to eat. (For your recovery diet, see Micronutrient.) Be sure, however, to keep up your fluid intake.

Take two aspirin.
Drugs known as antipyretics seek out the pyrogen and put it out of commission. Aspirin and acetaminophen are both antipyretics. However, do not give aspirin to a child who has or is suspected to have chicken pox, influenza, or even a minor respiratory illness, warns Imperato. This may trigger a potentially fatal condition known as Reyes syndrome, he adds. Stick with acetaminophen for children, and follow package directions carefully. ?

Dip.
If you feel uncomfortably warm, sponge yourself with tepid water or sit in a tub of shallow, tepid water and splash the water over your body. Don't fill the tub with water, since it's the evaporation of the water from the skin that helps cool you down. Make sure the water is not ice cold, which can be counterproductive, since it will cause shaking and make the fever rise again. Avoid alcohol altogether because it can be absorbed into the skin and cause intoxication and dehydration, advises Imperato.

Eat Yourself Well
As your fever breaks and you start feeling better, your appetite will improve. You may even feel ravenously hungry for a while. To restock your body's nutrient shelves, try eating a variety of foods, including fruits and vegetables, whole grains, low-fat dairy products, and low-fat meats, fish, and poultry The more variety in your diet, the likelier it is that you will provide your body with all of the nutrients it needs.
In spite of a sudden onset of appetite, however, remember one thing: If you haven't eaten much for a few days, your digestive system may need to be reacclimated, too. Eat, but not so much that you make yourself sick.