Fever, Adult

A fever is a higher than normal body temperature. In an adult, an oral temperature around 98.6° F (37° C) is considered normal. A temperature of 100.4° F (38° C) or higher is generally considered a fever. Mild or moderate fevers generally have no long-term effects and often do not require treatment. Extreme fever (greater than or equal to 106° F or 41.1° C) can cause seizures. The sweating that may occur with repeated or prolonged fever may cause dehydration. Elderly people can develop confusion during a fever.

A measured temperature can vary with:

  • Age.

  • Time of day.

  • Method of measurement (mouth, underarm, rectal, or ear).

The fever is confirmed by taking a temperature with a thermometer. Temperatures can be taken different ways. Some methods are accurate and some are not.

  • An oral temperature is used most commonly. Electronic thermometers are fast and accurate.

  • An ear temperature will only be accurate if the thermometer is positioned as recommended by the manufacturer.

  • A rectal temperature is accurate and done for those adults who have a condition where an oral temperature cannot be taken.

  • An underarm (axillary) temperature is not accurate and not recommended.

Fever is a symptom, not a disease.


  • Infections commonly cause fever.

  • Some noninfectious causes for fever include:

  • Some arthritis conditions.

  • Some thyroid or adrenal gland conditions.

  • Some immune system conditions.

  • Some types of cancer.

  • A medicine reaction.

  • High doses of certain street drugs such as methamphetamine.

  • Dehydration.

  • Exposure to high outside or room temperatures.

  • Occasionally, the source of a fever cannot be determined. This is sometimes called a "fever of unknown origin" (FUO).

  • Some situations may lead to a temporary rise in body temperature that may go away on its own. Examples are:

  • Childbirth.

  • Surgery.

  • Intense exercise.


  • Take appropriate medicines for fever. Follow dosing instructions carefully. If you use acetaminophen to reduce the fever, be careful to avoid taking other medicines that also contain acetaminophen. Do not take aspirin for a fever if you are younger than age 19. There is an association with Reye's syndrome. Reye's syndrome is a rare but potentially deadly disease.

  • If an infection is present and antibiotics have been prescribed, take them as directed. Finish them even if you start to feel better.

  • Rest as needed.

  • Maintain an adequate fluid intake. To prevent dehydration during an illness with prolonged or recurrent fever, you may need to drink extra fluid. Drink enough fluids to keep your urine clear or pale yellow.

  • Sponging or bathing with room temperature water may help reduce body temperature. Do not use ice water or alcohol sponge baths.

  • Dress comfortably, but do not over-bundle.


  • You are unable to keep fluids down.

  • You develop vomiting or diarrhea.

  • You are not feeling at least partly better after 3 days.

  • You develop new symptoms or problems.


  • You have shortness of breath or trouble breathing.

  • You develop excessive weakness.

  • You are dizzy or you faint.

  • You are extremely thirsty or you are making little or no urine.

  • You develop new pain that was not there before (such as in the head, neck, chest, back, or abdomen).

  • You have persistant vomiting and diarrhea for more than 1 to 2 days.

  • You develop a stiff neck or your eyes become sensitive to light.

  • You develop a skin rash.

  • You have a fever or persistent symptoms for more than 2 to 3 days.

  • You have a fever and your symptoms suddenly get worse.


  • Understand these instructions.

  • Will watch your condition.

  • Will get help right away if you are not doing well or get worse.