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Teen Version

What is a fever?

A fever means the body temperature is above normal. You have a fever if your oral temperature is over 99.5F (37.5C).

The body's average temperature when it is measured orally is 97.6F (36.5C), but it normally changes during the day. Oral temperature normally can change from a low of 95.8F (35.5C) in the morning to a high of 99.4F (37.5C) in the late afternoon. Mildly increased temperature (100.4 to 101.3F, or 38 to 38.5C) can be caused by exercise, heavy clothing, a hot bath, or hot weather. Warm food or drink can also raise the oral temperature. If you suspect such an effect on your temperature, take it again in a half hour.

How do I take my temperature?

  1. Shake the thermometer until it reads below 98.6F (37C), if you're using the glass-mercury type.
  2. Turn on the thermometer if you're using the digital type.
  3. Place the tip of the thermometer under one side of your tongue.
  4. Leave the thermometer in place for 3 minutes if you're using the glass-mercury type. For the digital type, wait until the thermometer signals that you can take it out.
  5. Read the thermometer where the line of mercury ends, or read the display on a digital thermometer.

What causes a fever?

Fever is a symptom, not a disease. It is the body's normal response to infections. Fever helps fight infections by turning on the body's immune system. The usual fevers (100 to 104F, or 37.8 to 40C) are not harmful. Most are caused by viral illnesses such as colds or flu. Some are caused by bacterial illnesses such as strep throat or bladder infections.

How long will it last?

Most fevers with viral illnesses range from 101F to 104F (38.3 to 40C) and last for 2 to 3 days. In general, the height of the fever doesn't relate to the seriousness of the illness. How sick you feel is what counts. Fever does not cause permanent harm until it reaches 107F (41.7C). Fortunately, the brain's thermostat keeps untreated fevers below this level.

How can I take care of myself?

  • Extra fluids and less clothing

    Drink extra fluids. Iced drinks are especially helpful. Body fluids are lost during fevers because of sweating.

    Dress in light clothing because most heat is lost through the skin. During the time you feel cold or are shivering (the chills), wrap yourself in a light blanket.

    If the fever is less than 102F this is the only treatment needed. Fever medicines are not necessary.

  • Medicines

    Remember that the fever is helping your body fight the infection. Take medicine only if your fever is over 102F (39C) and preferably only if you are also uncomfortable. You should take either acetaminophen or ibuprofen.

    Acetaminophen: Take any one of the acetaminophen products: Tylenol, Anacin-3, Panadol, or Tempra. The dosage is 2 tablets (650 mg) every 4 to 6 hours. 2 hours after they are taken, these drugs will reduce the fever 2 to 3F (1 to 2 C). Medicines do not bring the temperature down to normal unless the temperature was not very high before the medicine was given. Repeated dosages of the drugs will be necessary because the fever will go up and down until the illness runs its course.

    Ibuprofen: Ibuprofen is available in 200-mg tablets without a prescription as Advil, Motrin, etc. The dosage is 2 tablets (400 mg) of ibuprofen every 6 to 8 hours. When you use ibuprofen, stop taking acetaminophen.

    Avoid aspirin: Doctors recommend that anyone under age 21 years) not take aspirin if they have any symptoms of a cold or viral infection, such as a fever, cough, or sore throat. Aspirin taken during a viral infection, such as chickenpox or flu, has been linked to a severe illness called Reye's syndrome.

When should I call my health care provider?

Call immediately if:

  • Your fever is over 105F (40.6C).
  • You feel very sick.

Call within 24 hours if:

  • Your fever is between 104 and 105F (40 to 40.6C).
  • Your fever went away for more than 24 hours and then returned.
  • You have a fever for more than 3 days.
  • You have other concerns or questions.
Written by B.D. Schmitt, M.D., author of "Your Child's Health," Bantam Books.
Published by McKesson Provider Technologies.
Last modified: 2006-07-31
Last reviewed: 2006-02-23
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright 2006 McKesson Corporation and/or one of its subsidiaries. All Rights Reserved.
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