Fever is the temporary increase in the body's temperature in response to some disease or illness.
A child has a fever when the temperature is at or above one of these levels:
An adult probably has a fever when the temperature is above 99 - 99.5 °F (37.2 - 37.5 °C), depending on the time of day.
Normal body temperature may change during any given day. It is usually highest in the evening. Other factors that may affect body temperature are:
Fever is an important part of the body's defense against infection. Most bacteria and viruses that cause infections in people thrive best at 98.6 °F. Many infants and children develop high fevers with minor viral illnesses. Although a fever signals that a battle might be going on in the body, the fever is fighting for the person, not against.
Brain damage from a fever generally will not occur unless the fever is over 107.6 °F (42 °C). Untreated fevers caused by infection will seldom go over 105 °F unless the child is overdressed or trapped in a hot place.
Febrile seizures do occur in some children. However, most febrile seizures are over quickly, do not mean your child has epilepsy, and do not cause any permanent harm..
Unexplained fevers that continue for days or weeks are called fevers of undetermined origin (FUO).
Almost any infection can cause a fever. Some common infections are:
Children may have a low-grade fever for 1 or 2 days after some immunizations.
Teething may cause a slight increase in a child's temperature, but not higher than 100 °F.
Autoimmune or inflammatory disorders may also cause fevers. Some examples are:
Other possible causes of fever include:
A simple cold or other viral infection can sometimes cause a high fever (102 - 104 °F, or 38.9 - 40 °C). This does not usually mean you or your child have a serious problem. Some serious infections may cause no fever or even a very low body temperature, especially in infants.
If the fever is mild and you have no other problems, you do not need treatment. Drink fluids and rest.
The illness is probably not serious if your child:
Take steps to lower a fever if you or your child is uncomfortable, vomiting, dried out (dehydrated), or not sleeping well. Remember, the goal is to lower, not eliminate, the fever.
When trying to lower a fever:
Here are some guidelines for taking medicine to lower a fever:
Eating and drinking with a fever:
Call a doctor right away if your child:
Call 911 if you or your child has a fever and:
Call your doctor right away if you are an adult and you:
Your doctor will perform a physical examination, which may include a detailed examination of the skin, eyes, ears, nose, throat, neck, chest, and abdomen to look for the cause of the fever.
Treatment depends on the duration and cause of the fever, as well as your other symptoms.
The following tests may be performed:
Elevated temperature; Hyperthermia; Pyrexia
Mick NW. Pediatric fever. In: Marx JA, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 7th ed. Philadelphia, PA: Mosby Elsevier; 2009:chap 165.
Leggett J. Approach to fever or suspected infection in the normal host. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 288.
Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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