Fever is a higher-than-normal body temperature. A normal temperature varies with:

  • Age.

  • How it is measured (mouth, underarm, rectal, or ear).

  • Time of day.

In an adult, an oral temperature around 98.6° Fahrenheit (F) or 37° Celsius (C) is considered normal. A rise in temperature of about 1.8° F or 1° C is generally considered a fever (100.4° F or 38° C). In an infant age 28 days or less, a rectal temperature of 100.4° F (38° C) generally is regarded as fever. Fever is not a disease but can be a symptom of illness.


  • Fever is most commonly caused by infection.

  • Some non-infectious problems can cause fever. For example:

  • Some arthritis problems.

  • Problems with the thyroid or adrenal glands.

  • Immune system problems.

  • Some kinds of cancer.

  • A reaction to certain medicines.

  • 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.

  • Some situations may cause a rise in body temperature but these are not considered "true fever". Examples are:

  • Intense exercise.

  • Dehydration.

  • Exposure to high outside or room temperatures.


  • Feeling warm or hot.

  • Fatigue or feeling exhausted.

  • Aching all over.

  • Chills.

  • Shivering.

  • Sweats.


A fever can be suspected by your caregiver feeling that your skin is unusually warm. 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:

With adults, adolescents, and children:

  • An oral temperature is used most commonly.

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

  • Under the arm temperatures are not accurate and not recommended.

  • Most electronic thermometers are fast and accurate.

Infants and Toddlers:

  • Rectal temperatures are recommended and most accurate.

  • Ear temperatures are not accurate in this age group and are not recommended.

  • Skin thermometers are not accurate.


  • During a fever, the body uses more oxygen, so a person with a fever may develop rapid breathing or shortness of breath. This can be dangerous especially in people with heart or lung disease.

  • The sweats that occur following a fever can cause dehydration.

  • High fever can cause seizures in infants and children.

  • Older persons can develop confusion during a fever.


  • Medications may be used to control temperature.

  • Do not give aspirin to children with fevers. There is an association with Reye's syndrome. Reye's syndrome is a rare but potentially deadly disease.

  • If an infection is present and medications have been prescribed, take them as directed. Finish the full course of medications until they are gone.

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

  • Do not over-bundle children in blankets or heavy clothes.

  • Drinking adequate fluids during an illness with fever is important to prevent dehydration.


  • For adults, rest and adequate fluid intake are important. Dress according to how you feel, but do not over-bundle.

  • Drink enough water and/or fluids to keep your urine clear or pale yellow.

  • For infants over 3 months and children, giving medication as directed by your caregiver to control fever can help with comfort. The amount to be given is based on the child's weight. Do NOT give more than is recommended.


  • You or your child are unable to keep fluids down.

  • Vomiting or diarrhea develops.

  • You develop a skin rash.

  • An oral temperature above 102° F (38.9° C) develops, or a fever which persists for over 3 days.

  • You develop excessive weakness, dizziness, fainting or extreme thirst.

  • Fevers keep coming back after 3 days.


  • Shortness of breath or trouble breathing develops

  • You pass out.

  • You feel you are making little or no urine.

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

  • You cannot hold down fluids.

  • Vomiting and diarrhea persist for more than a day or two.

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

  • An unexplained temperature above 102° F (38.9° C) develops.