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Fever in adults

September 18, 2022

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

Serious sad aged woman holding a thermometer.

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

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.

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.

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 types of cancers.

Fever symptoms

People with a fever may also:

  • sweat
  • shiver (chills)
  • have a headache
  • have achy muscles
  • not want to eat
  • break out in a rash
  • be restless
  • feel weak.

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 travel abroad.

Treating a fever

Fever is part of your body's defense against infection-causing germs. By itself, fever is usually harmless, though a high fever can be miserable. 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.
  • Get plenty of rest.
  • 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.
  • Dress lightly (even if you have chills).

If you have a fever over 104°F (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
  • confusion
  • 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
  • pain when urinating or urine that smells bad

Image: yacobchuck/Getty Images


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No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

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