What is a fever?

A fever is a body temperature that is higher than normal. It usually means there is an abnormal process occurring in the body. Exercise, hot weather, and common childhood immunizations can also make body temperature rise.

What causes a fever?

A fever is not an illness by itself. Rather it is a symptom that something is not right within the body. A fever does not tell you what is causing it, or even that a disease is present. It may be a bacterial or viral infection. Or, it could be a reaction from an allergy to food or medicine. Becoming overheated at play or in the sun can also result in fever.

What are the symptoms of a fever?

Normal body temperature ranges from 97.5°F to 98.9°F (36.4°C to 37.2°C). It tends to be lower in the morning and higher in the evening. Most healthcare providers consider a fever to be 100.4°F (38°C) or higher. High fevers may bring on seizures or confusion in children. It's not how high the temperature is, but how fast the temperature goes up that causes a seizure.


  • Flushed face
  • Hot, dry skin
  • Low output of urine, or dark urine
  • Not interested in eating
  • Constipation or diarrhea
  • Vomiting
  • Headache
  • Aching all over
  • Nausea

How is a fever diagnosed?

  • Temporal artery (temperature taken across the forehead area)


Most thermometers today are digital, but there are some glass thermometers containing mercury still in use. Mercury is toxic substance and is dangerous to humans and the environment. Because glass thermometers can break, they should be disposed of properly in accordance with local, state, and federal laws. For information on how to safely dispose of a mercury thermometer, contact your local health department, waste disposal authority, or fire department.

How is a fever treated?

You can treat a fever with acetaminophen or ibuprofen in dosages advised by your healthcare provider. Switching between giving acetaminophen and ibuprofen can cause medicine errors and may lead to side effects. Never give aspirin to a child or young adult who has a fever.


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

When should I call my healthcare provider?


Call right away or seek immediate medical attention if any of the following occur with a fever:

  • Seizure
  • Feeling dull or sleepy
  • Irregular breathing
  • Stiff neck
  • Confusion
  • Purple spotted rash
  • Sore throat that persists
  • Vomiting
  • Diarrhea
  • Painful, burning, or frequent urination

Key points about fevers

  • A fever is not an illness by itself, but, rather, a sign that something is not right within the body.
  • Illness, exercise, hot weather, and common childhood immunizations can make body temperature rise.
  • Call your healthcare provider if a baby under 3 months has a fever, or seek immediate medical attention if a fever is accompanied by a seizure, lethargy, irregular breathing, stiff neck, confusion, or other signs of a serious illness.

Next steps


  • Before your visit, write down questions you want answered.
  • Ask if your condition can be treated in other ways.

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