Infection is a common cause of fever, but other conditions can also bring heat.


Fever is one of the body's most effective ways of fighting infection.

Fever means a body temperature of 100.4° F (38°C) or higher. An infection, such as the flu, is the most common cause of fever.

The average body temperature is 98.6° F (37°C). But "normal" body temperature varies from person to person. It also changes during the day, rising a bit after you eat or exercise. Body temperature is often higher in the afternoon than it is when you wake up in the morning.

Other conditions can also cause a fever. These include diseases that produce inflammation, such as rheumatoid arthritis; reactions to drugs or vaccines; and even certain cancers.

Fever symptoms

People with a fever may also:
  • shiver (chills)
  • be restless
  • sweat
  • feel weak.
  • not want to eat
A very high fever can cause confusion, extreme sleepiness, irritability, and seizures.

Diagnosing the cause of a fever

To help determine why you have a fever, your doctor will ask you about:
  • other symptoms such as coughing, abdominal pain, vomiting, diarrhea, or pain when urinating
  • recent surgeries or injuries
  • recent vaccinations
  • new drugs you may be taking
  • recent travel particularly travels abroad.

Treating a fever

Fever is part of your body's defense against infection-causing germs. These steps may help you feel better:
  • Drink plenty of fluids to help cool your body and prevent dehydration.
  • Eat light foods that are easy to digest.
  • Take ibuprofen (Advil, Motrin, or others), naproxen (Aleve, Naprosyn, or others), acetaminophen (Tylenol, others), or aspirin to help relieve head and body aches and lower your temperature.
  • Take a slightly warm, not cool bath, or apply damp washcloths to the forehead and wrists.
If you have a fever over 40°C, call your doctor. Call your doctor right away if you have a fever along with any of these symptoms:
  • seizure
  • loss of consciousness
  • stiff neck
  • trouble breathing
  • severe pain anywhere in the body
  • swelling or inflammation of any part of the body
  • vaginal discharge that is discolored or smells bad
Credit: Harvard Health Publishing