Topic Overview Fever is the body's normal and healthy reaction to infection and other illnesses, both minor and serious. Fevers cause the immune system to increase the production of white blood cells and other substances that help fight infection. Fever is a symptom, not a disease. In most cases fever means you have a minor illness. Often the importance of a fever can be determined only when other symptoms are evaluated. Normal body temperature Average normal body temperature is 98.6° (37°) orally. It usually varies during the day from a low of 97.4° (36.33°) in the morning to a high of 99.6° (37.56°) in the late afternoon. Exercising, wearing too many clothes, taking a hot bath, or being out in hot weather can cause an increase in your temperature. Fever temperatures A fever is a high body temperature. A temperature of up to 102° (38.89°) can be helpful, because it helps the body react to an infection. Most healthy children and adults can tolerate a fever as high as 103° (39.44°) to 104° (40°) for short periods of time without problems. In some situations, you may not be able to measure your temperature. It is important to look for other symptoms of illness while you have a fever. Children tend to run higher fevers than adults. The degree of fever may not indicate how serious the illness is. With a minor illness, such as a cold, you may have a temperature, while a very serious infection may cause little or no fever. It is important to look for other symptoms along with the fever. A fever without other symptoms that lasts 3 to 4 days, comes and goes, and gradually reduces over time is usually not a cause for concern. When you have a fever, you may feel tired, lack energy, and may not eat as much as usual. High fevers are not comfortable, but they rarely cause serious problems. Temperatures in this topic are oral temperatures. Oral temperatures are usually taken in older children and adults. Oral temperature taken after smoking or drinking a hot fluid may give you a false high temperature reading. Rectal temperatures are the most accurate, especially in young children. Ear probe thermometers are used often but are generally less accurate. Temperature color strips on the skin are not accurate and should not be used to measure a fever. For information on how to take an accurate temperature, see the topic Body Temperature. Causes of fever Most infections with a fever are caused by: Viral infections, such as colds and flu.
Bacterial infections, such as a urinary tract infection or pneumonia.
It is important to look for other symptoms along with the fever. Travel outside your native country can also expose you to other diseases found around the world. Fevers that begin after traveling in other countries need to be evaluated by your health professional. In the United States, the Centers for Disease Control and Prevention (CDC) have extensive information on infectious diseases around the world. See the Other Places to Get Help section of this topic. Treating a fever In most cases, the illness that caused the fever will clear up in a few days. You usually can treat the fever at home if you: Are in good health without any medical problems.
Don't have other significant symptoms with the fever.
Are taking in enough food and fluids.
Are urinating normal amounts.
Seem to be improving.
For specific fever guidelines for children age 3 and younger, see the topic Fever, Age 3 and Younger.
Review the Emergencies and Check Your Symptoms sections to
determine if and when you need to see a health professional.
| 
