Fever is the body's normal and healthy
reaction to infection and other illnesses, both minor and serious. It helps the
body fight infection. Fever is a symptom, not a disease. In most cases, having
a fever means you have a minor illness. When you have a fever, your other
symptoms will help you determine how serious your illness is.
Temperatures in this topic are oral temperatures. Oral
temperatures are usually taken in older children and adults.
Normal body temperature
Most people have an average
body temperature of about
98.6�F (37�C), measured orally
(a thermometer is placed under the tongue). Your temperature may be as low as
97.4�F (36.3�C) in the morning
or as high as 99.6�F (37.6�C)
in the late afternoon. Your temperature may go up when you exercise, wear too
many clothes, take a hot bath, or are exposed to hot weather.
A fever is a high body
temperature. A temperature of up to
102�F (38.9�C) can be helpful
because it helps the body fight infection. Most healthy children and adults can
tolerate a fever as high as
103�F (39.4�C) to
104�F (40�C) for short periods
of time without problems. Children tend to have higher fevers than
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 and evaluate other symptoms along with the fever.
are not able to measure your temperature with a thermometer, you need to
look for other symptoms of illness. 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
not eat as much as usual. High fevers are not comfortable, but they rarely
cause serious problems.
Oral temperature taken after smoking or
drinking a hot fluid may give you a false high temperature reading. After
drinking or eating cold foods or fluids, an oral temperature may be falsely
low. For information on how to take an
accurate temperature, see the topic
Causes of fever
Viral infections, such as colds and
bacterial infections, such as a
urinary tract infection or
pneumonia, often cause a fever.
outside your native country can expose you to other diseases. Fevers that begin
after travel in other countries need to be evaluated by your doctor.
Fever and respiratory symptoms are hard to
evaluate during the flu season. A fever of
102�F (38.9�C) or higher for 3
to 4 days is common with the flu. For more information, see the topic
Respiratory Problems, Age 12 and Older.