Fever is a higher-than-normal body temperature.
Normal body temperature changes during the day. Exercise, stress, or dehydration may cause a person's temperature to go up temporarily. If temperature returns to normal when the person is rested and hydrated, there is usually no reason to look for other causes.
Fever is a symptom, not a disease. A fever may mean that there is something else going on in the body that is causing it. A higher body temperature gives the immune system an advantage in fighting bacteria and viruses because most of them do not survive well at higher temperatures.
The signs and symptoms of a fever depend on what is causing it. At first, a fever can cause a chill. When the brain raises the body's "thermostat," the body responds by shivering to raise the temperature. Shivering produces heat in the body. Once the temperature goes up, the person often feels warm. When the brain then lowers the thermostat, the person may start to sweat to bring the temperature down.
Fever can be caused by almost any infectious condition. Some of the more common in otherwise healthy individuals in the U.S. include strep throat caused by group A strep, pneumonia caused by Mycoplasma or Streptococcus pneumoniae, influenza ("the flu"), chickenpox, the common cold, ear infections in children, or urinary tract infections in adult women. In parts of Asia and Africa, malaria is the first thing to suspect if a person has a high fever.
Not all causes of fever are infections. Other causes include tissue injuries, some types of cancer, inflammatory diseases, or being in a hot environment for too long. The main risk of mild or moderate fevers is dehydration, because people need more fluids than usual when they have a fever.
A fever greater than 106 degrees Fahrenheit can result in brain damage and death in some cases. This level of fever is hardly ever brought on by common illnesses. It can be seen in bacterial meningitis, in a rare reaction to anesthesia called malignant hyperthermia, or if a person is in a situation where he or she cannot cool himself or the body's temperature regulation mechanism has failed (heat stroke).
Fever in children presents special concerns for parents, since some children have febrile seizures with fever. Rarely, these can lead to injury to the child, but this is rare.
Generally, nothing should be done to prevent fevers because they are an important signal to what might be wrong with the body. Some causes can be prevented, for example, a person should avoid staying in a hot environment for too long. It is very important to drink more fluids than usual after heavy exercise, especially when it is hot outside.
A thermometer is used to measure the temperature. The temperature can be taken in the mouth, rectum, or ear. When measured in the rectum, the temperature is about a half degree C higher than in the mouth. If necessary, the temperature can also be measured under the arm or on the skin, though readings at these sites are less accurate.
Mild or moderate fever generally has no long-term effects. The dehydration caused by fever can be avoided by drinking extra fluids. Fevers greater than 106 degrees F can sometimes result in brain damage or death if the fever is not treated within several hours.
A person with a fever may have an infection that is contagious. If other conditions are causing the fever, there are no risks to others.
If possible, treatment is usually directed first at whatever is causing the fever. Most bacterial infections, for instance, are treated with antibiotics. Most common viral infections, on the other hand, cannot be treated except to relieve symptoms.
If the cause is known, it makes sense to reduce the person's discomfort by bringing a moderate fever down. Acetaminophen (i.e., Tylenol) or ibuprofen (i.e., Advil, Motrin) are useful for this purpose. Because a fever may return after the first dose of medication, doses should be taken as directed throughout the day. Extra fluids should be taken to help avoid dehydration.
For a very high fever, bringing the temperature down is an immediate priority regardless of the cause, in order to prevent brain damage. Sponging or bathing in lukewarm water can reduce body temperature by cooling the skin.
Ice water or alcohol sponge baths are no more effective than lukewarm water, so these should never be used.
Extra clothing and blankets should not be used because they will only cause the fever to rise. Fevers greater than 106 degrees F are very serious and must be treated in the hospital.
Aspirin should not be given to anyone under 18 years of age except under the direction of a healthcare professional. This is because a rare condition called Reye's syndrome , a severe inflammation of the brain and liver, has been linked to aspirin use in young people, especially, but not always, in cases of the flu and chickenpox.
Every medication has its own set of side effects, of which allergic reactions and stomach upset are two of the most common.
What happens after treatment depends on what caused the fever. If the cause of the fever is corrected, the fever generally goes away. Further treatment may not be required.
The temperature can be taken at regular intervals to monitor the fever. How long to continue monitoring depends on how long the fever lasts and on its underlying cause
Harrison's Principles of Internal Medicine, 1998, Fauci et al.