Symptom Definition

  • Rectal temperature greater than 100.4°F (38.0°C)
  • Oral temperature greater than 99.5 F (37.5 C)
  • Ear (tympanic) temperature greater than 99.5 (37.5 C), when in oral mode
  • Forehead temperature strips are unreliable

General Information

  • In most clinical situations, fever does no major harm, and may actually benefit the human body by helping it to fight off infection. Nevertheless, fever is an abnormal finding. It can signal a serious illness, especially in adults who are old, frail, or have a weakened immune system.
  • Adults tend to run lower fevers than children. Fever may be further blunted or even absent in elderly patients.
  • Fever itself can cause muscle aches, nausea, lightheadedness, weakness and headache.

Normal Body Temperature

  • 98.6 F (37 C) is the oral temperature that most physicians, nurses, laypersons, and medical references state is "normal."
  • The average temperature of healthy elderly patients is the same as younger adults. However, there is some data to suggest that the average temperature in chronically ill elderly patients is lower than that of other healthy adults. Thus, interpretation of a temperature reading in a chronically ill elderly adult must be done with caution. Because lower baseline temperatures can be expected in this group of patients, it may be easy to miss a fever if the conventional fever definition is used.

Normal Variations in Body Temperature

  • There is a normal daily awake-sleep cycle variation in temperature, with the low occurring at 6 AM and the high occurring at 6 pm. The low and high temperatures vary by 0.9 F (0.6 C).
  • In women, temperature increases about 0.9 F (0.6 C) at the time of ovulation.
  • Temperature can go up in response to physical activity, particularly during hot weather.

See More Appropriate Topic (instead of this one) If


Call 911 Now (you may need an ambulance) If:

  • Difficult to awaken or acting confused
  • Very weak (can't stand)
  • Severe difficulty breathing (e.g. struggling for each breath, unable to speak)
  • Lips or face are bluish now
  • Rash with purple (blood-colored) spots or dots

Call Your Doctor Now (night or day) If:

  • You feel weak or very sick
  • Fever of 103 F (39.4 C) or higher
  • Fever of 100.5 F (38.1 C) or higher and you  
    • Are over 60 years of age
    • Have diabetes mellitus or a weakened immune system (e.g. HIV positive, cancer chemotherapy, chronic steroid treatment, splenectomy)
    • Are bedridden (e.g. nursing home patient, stroke, chronic illness, recovering from surgery)
    • Are a transplant patient (e.g. liver, heart, lung, kidney)
  • Headache and stiff neck (can't touch chin to chest)
  • Difficulty breathing
  • Signs of dehydration (e.g. no urine in more than 12 hours, very dry mouth, lightheaded, etc.)
  • Have an intravenous catheter (e.g. central line, PICC, or peripheral intravenous line)

Call Your Doctor Within 24 Hours (between 9am and 4pm) If:

  • You think you need to be seen
  • Fever of 100.5 F (38.1 C) or higher and you have traveled to a foreign country in the last month
  • Fever lasts longer than 3 days (72 hours)

Call Your Doctor During Weekday Office Hours If:

  • You have other questions or concerns

Self Care at Home If:

  • Fever with no signs of serious infection and you don't think you need to be seen


  1. Reassurance: Most fevers are good, because they help the body fight infection. The goal of fever therapy is to bring the fever down to a comfortable level. Use the following definitions to help put your level of fever into perspective:
    • 99.5 - 101 F Oral Low-grade fevers and beneficial (37.5 - 38.3 C)  
    • 101 - 103 F Oral  Moderate-grade fevers and beneficial (38.3 - 39.4 C)
    • 103 - 105 F Oral High fever that causes headache and malaise, generally harmless in healthy adults, but higher risk of bacterial infection (39.4 - 41.7 C)
    • Over 105 F Oral Very high fever (> 41.7 C)
  2. For All Fevers:
    • Give cold fluids orally to prevent dehydration. (Reason: good hydration replaces sweat and improves heat loss via skin) Adults should drink 6-8 glasses of water daily.
    • Dress in 1 layer of lightweight clothing and sleep with 1 light blanket.
    • For fevers 100-101 F (37.8-38.3 C), this is the only treatment and fever medicine is unnecessary.
  3. Fever Medicine: For fevers above 101 F (38.3 C) take acetaminophen every 4-6 hours (e.g. Tylenol; adult dosage 650 mg) or ibuprofen every 6-8 hours (e.g. Advil, Motrin; adult dosage 400 mg). The goal of fever therapy is to bring the fever down to a comfortable level. Remember that fever medicine usually lowers fever 2 degrees F (1 - 1 1/2 degrees C).
    • Do not take ibuprofen if you have stomach problem, kidney disease, are pregnant, or have been told by your doctor to avoid this type of anti-inflammatory drug. Do not take ibuprofen for more than 7 days without consulting your doctor.
    • Do not take acetaminophen if you have liver disease.
    • Read the package instructions thoroughly on all medications that you take.
  4. Lukewarm Shower for Reducing Fever: Take the fever medicine first. Take a lukewarm shower or bath for 10 minutes. Lukewarm water should be warm enough that it does not make you shiver, but cold enough that it helps cool you off and reduce your temperature.  Do not sponge yourself with rubbing alcohol.
  5. Expected Course: Most fevers from a viral illness such as a cold fluctuate between 99.5 and 103 F (37.5 - 39.5 C) and last for 2 or 3 days.
  6. Contagiousness: You can return to work or school after the fever is gone.
  7. Call Your Doctor If:
    • Fever lasts longer than 3 days (72 hours)
    • You become worse or develop any of the "Call Doctor Now" symptoms.

Disclaimer: This information is not intended be a substitute for professional medical advice. It is provided for educational purposes only. You assume full responsibility for how you choose to use this information.

Adult HouseCalls Online. Copyright © 2000-2004 David Thompson, M.D. FACEP

Reviewed 8/2004

Revised 8/2003

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