Diseases & Conditions

Fever

A fever is usually a sign that something out of the ordinary is going on in your body. For an adult, a fever may be uncomfortable, but usually isn't dangerous unless it reaches 103 F (39.4 C) or higher. For young children and infants, a slightly elevated temperature may indicate a serious infection.

But the degree of fever doesn't necessarily indicate the seriousness of the underlying condition. A minor illness may cause a high fever, and a more serious illness may cause a low fever.

Usually a fever goes away within a few days. A number of over-the-counter medications lower a fever, but sometimes it's better left untreated. Fever seems to play a key role in helping your body fight off a number of infections.

Your normal body temperature varies throughout the day according to circadian rhythm — it's lower in the morning and higher in the late afternoon and evening. In fact, your normal temperature can range from about 97 F (36.1 C) to 99 F (37.2 C). Although most people consider 98.6 F (37 C) normal, your temperature may vary by a degree or more. Other factors, such as your menstrual cycle or heavy exercise, can affect your temperature.

Here's how body temperature works:

• Your body temperature is set by your hypothalamus, an area at the base of your brain that acts as a thermostat for your whole system.
• Your temperature is the balance of the heat produced by your body tissues, particularly your liver and muscles, and the heat your body loses.
• When you're ill, your normal temperature may be set a few points higher as your body directs blood away from your skin to decrease heat loss.
• When a fever starts and your body tries to elevate its temperature, you feel chilly and may shiver to generate heat until the blood around your hypothalamus reaches the new set point.
• When your temperature begins to return to normal, you may sweat profusely to get rid of the excess heat.
• If you're very old, very young or alcoholic, your body's ability to produce a fever may be lessened.

A fever usually means your body is responding to a viral or bacterial infection. Other possible causes include:

• Heat exhaustion
• Extreme sunburn
• Certain inflammatory conditions such as rheumatoid arthritis — inflammation of the lining of your joints (synovium)
• Malignant tumor or some forms of kidney cancer (rare)
• Some medications, such as antibiotics and drugs used to treat high blood pressure or seizures
• Some immunizations, such as the diphtheria, tetanus and acellular pertussis (DTaP) or pneumococcal vaccines (in infants and children)

Sometimes it's not possible to identify the cause of a fever. If you have a temperature of 101 F (38.3 C) or higher for more than three weeks and your doctor isn't able to find the cause after extensive evaluation, the diagnosis may be fever of unknown origin.

Your doctor will look for an infection or noninfectious cause of your fever based on your other symptoms and a physical exam. You may need tests, such as blood tests, to confirm a diagnosis.

If you have a low-grade fever that persists for three weeks or more, but have no other symptoms, your doctor may recommend a variety of tests to help find the cause. These may include blood tests and X-rays.

A rapid rise or fall in temperature may cause a fever-induced seizure (febrile seizure) in a small number of children ages 6 months to 5 years. Although alarming for parents, the vast majority of febrile seizures cause no lasting effects.

Febrile seizures usually involve loss of consciousness and shaking of limbs on both sides of the body. Less commonly, a child may become rigid and twitch only part of his or her body. If a seizure occurs, lay your child on his or her side or stomach on the floor or ground. Remove any sharp objects that are near your child, loosen tight clothing and hold your child to prevent injury. Don't place anything in your child's mouth or try to stop the seizure. Although most seizures stop on their own, call for emergency medical assistance if a seizure lasts longer than 10 minutes.

Take your child to the doctor as soon as possible after the seizure to determine the cause of the fever.

Treatment depends on the cause of your fever. Your doctor will likely prescribe antibiotics for bacterial infections, such as pneumonia or strep throat.

Antibiotics don't treat viral infections, such as stomach infection (gastroenteritis) and mononucleosis. There are a few antiviral drugs used to treat some specific viral infections. However, the best treatment for most viruses is often rest and plenty of fluids.

Over-the-counter medications
Your doctor may also make a recommendation about using over-the-counter medications, such as acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin, others) to lower a high fever. Adults also may use aspirin. Don't give aspirin to children, however, because it may trigger a rare, but potentially fatal, disorder known as Reye's syndrome.

The downside of lowering a fever
If you have a low-grade fever, it's not advisable to try to lower your temperature. Doing so may prolong the illness or mask your symptoms and make it harder to determine the cause.

Some experts believe that aggressively treating a fever interferes with your body's immune response. The viruses that cause colds and other respiratory infections thrive at normal body temperature. By producing a low-grade fever, your body may be helping eliminate a virus.