What is fever?

Fever (also called pyrexia) is defined as body temperature that is higher than normal for each individual. It generally indicates that there is an abnormal process occurring in the body. Exercise, hot weather, and common childhood immunizations can also make body temperature rise.

Fever is not an illness by itself, but, rather, a symptom or an indicator that something is not right within the body. A fever does not tell you what disorder is causing it, or even that a disease is present. It may be a bacterial or viral infection, or a reaction from an allergy to food or medication, or becoming overheated at play or in the sun.

What constitutes a fever?

Normal body temperature ranges from 97.5 to 98.9 degrees Fahrenheit (36.4 to 37.2 degrees Celsius) and tends to be lower in the morning and higher in the evening. Most health care providers consider a fever to be 100.4 degrees Fahrenheit (38 degrees Celsius) or higher. Although high fevers may bring on seizures (convulsions) in children or confusion, generally, it is not how high the temperature is, but how rapidly the temperature rises that causes a convulsion.

What are the signs that indicate fever?

In addition to taking a person's temperature with a thermometer, look for other signs (outward indications) of fever. This is especially important because a baby, young child, or disabled person may not be able to express how he or she is feeling because a baby, young child, or disabled person may not be able to express how he or she is feeling. Signs that indicate fever may include the following:

  • Flushed face

  • Hot, dry skin

  • Low output of urine, and/or dark urine

  • Not interested in eating

  • Constipation or diarrhea

  • Vomiting

  • Headache

  • Aching all over

  • Nausea

Taking the temperature

The best means of taking temperature is with a thermometer. There are several types of thermometers, including the following:

  • Digital thermometer (oral, rectal, or axillary)

  • Ear thermometer (not recommended in babies younger than 3 months of age) 

Taking a temperature rectally is the most accurate method in children under 3 years of age. Axillary (under the armpit) or oral (in the mouth) methods can be used for older children and adults. Talk with your health care provider about the best way to take your temperature.  

About glass thermometers containing mercury

Most thermometers today are digital, but there are some glass thermometers containing mercury still in use. According to the EPA, mercury is a toxic substance that poses a threat to the health of humans, as well as to the environment. Because of the risk of breaking, glass thermometers containing mercury should be removed from use and disposed of properly in accordance with local, state, and federal laws. Contact your local health department, waste disposal authority, or fire department for information on how to properly dispose of mercury thermometers.

Treating fever

Once you have determined that the person has a fever, you may treat it by giving acetaminophen or ibuprofen in dosages advised by your health care provider. Alternating between giving acetaminophen and ibuprofen can cause medication errors and may lead to side effects. Never give aspirin to a child or young adult who has a fever.

A tepid bath (water is neither too cool nor too warm to the touch) may reduce the fever, as well as comfort the person. Alcohol rubdowns are no longer recommended.

Call your health care provider for guidance anytime you are uncomfortable with the conditions of the fever, and remember to contact your health care provider any time a temperature spikes rapidly or persists despite treatment.

When to call your health care provider

Call your health care provider immediately if any of the following conditions accompany a fever:

  • Fever in a baby younger than 3 months old 

  • Seizure

  • Feeling dull or sleepy

  • Irregular breathing

  • Stiff neck

  • Confusion

  • Purple spotted rash

  • Ear pain (a child tugging on his or her ear)

  • Sore throat that persists

  • Vomiting

  • Diarrhea

  • Painful, burning, or frequent urination