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March 2009
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Too Hot to Handle?
Facts About Fevers

Cartoon of woman holding her forehead and reading a thermometer

You know the feeling. You’re achy and run down. Something’s not quite right. When you finally get home and reach for the thermometer, you soon find that your temperature’s above normal. You have a fever—a sign that something is out of balance in your body.

Fevers aren’t necessarily bad. In fact, by turning up the heat, a fever can help you fight off disease-causing bacteria and viruses, which tend to grow and flourish at the body’s normal temperature. Fever also activates your body’s immune system, which protects you against infection.

Normal body temperature is considered to be 98.6 degrees Fahrenheit. “But in reality there’s a lot of individual variation in the ‘normal’ temperature,” says Dr. Fred Gill, chief of the internal medicine consult service at NIH’s Clinical Center. “Body temperature often fluctuates throughout the day. It tends to be higher in the afternoon and early evening and is typically lower in the middle of the night. A slight rise in temperature without other symptoms does not necessarily mean you have a fever.”

In general, doctors don’t consider you to have a fever until your temperature reaches 100.4 degrees. Fever can make you feel uncomfortable and have trouble sleeping, but it’s rarely dangerous in adults. It’s different for infants under 3 months old. They should be evaluated by a doctor for any fever that reaches 100.4 degrees.

Fever often brings the shivers. You feel chilled because blood vessels in your skin tighten and shrink, keeping warm blood deeper within your body and making your skin feel cold. As a result, your muscles contract and you shiver. Fevers often start to subside when you begin to sweat. Sweating is good because it helps your body cool down and return your temperature to normal.

Infections are the most common cause of fever, but there are many other triggers. Toxins, certain medications, cancer and diseases that weaken the immune system are a few of the things that can cause your temperature to rise.

Fever in children between 6 months and 5 years of age can sometimes cause febrile (fever-induced) seizures. During a febrile seizure, a child often loses consciousness and shakes. Most seizures last just a minute or 2. Although they can be frightening to parents, febrile seizures are usually harmless.

In general, if a fever is mild and you have no other major symptoms, simply drink fluids and get plenty of rest. If a child with a fever is comfortable, drinking liquids and sleeping well, no treatment is needed.

Over-the-counter medicines like ibuprofen or acetaminophen can help to control discomfort. Adults can generally take aspirin, but children and teens with fever should avoid it because aspirin increases the risk of a rare and sometimes deadly disease called Reye’s syndrome.

When giving children medication, follow your pediatrician’s recommendation. Check the label as well to make sure you’re giving the right dose for your child’s weight.


Definitions iconDefinitions

Immune System
The system that protects your body from invading viruses, bacteria and other microscopic threats.

Wise Choices iconWise Choices

Know When to Call a Doctor

Adults, contact a doctor if:

  • your body temperature is
    above 103 degrees Fahrenheit.
  • your temperature is 100.4
    degrees or higher for more
    than 3 days.

Call your doctor if these symptoms accompany a fever:

  • Severe headache
  • Unusual skin rash
  • Neck stiffness or pain
  • Confusion
  • Persistent vomiting
  • Difficulty breathing or chest pain
  • Abdominal pain or pain
    when urinating
  • Blood in stool

Links iconWeb Sites


Febrile Seizures 

Reye's Syndrome  

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