Fever in adults: When to worry

Fever is one of the body's most effective ways of fighting infection. It is part of your body's defense against infection-causing germs.

You get a fever most often when your body is trying to kill infectious invaders such as viruses or bacteria. A higher body temperature helps the immune system respond more vigorously to the attack, and makes it harder for these microbes to survive.

What is considered a fever in adults?

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.

High fever in adults

While any temperature above your normal temperature range is considered a fever, there are different levels of fever severity:

• Low-grade: 99.1 to 100.4 F (37.3 to 38.0 C)
• Moderate-grade: 100.6 to 102.2 F (38.1 to 39.0 C)
• High-grade: 102.4 to 105.8 F (39.1 to 41 C).

When to worry about fever

If you have a fever over 104°F (40°C), you should call your doctor.

Seek medical help 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.

Causes of fever

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.

Accompanying symptoms

The following symptoms may also accompany fever:

• sweats
• chills
• headache
• achy muscles
• lack of desire to eat
• rash
• restlessness
• weakness.

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.

How to treat a fever at home

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), or acetaminophen (Tylenol, others) 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.

Image: yacobchuck/Getty Images