Fever is the temporary increase in the body's temperature in response to a 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°F to 99.5°F (37.2°C to 37.5°C), depending on the time of day.
Elevated temperature; Hyperthermia; Pyrexia; Febrile
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 (37°C). Many infants and children develop high fevers with mild viral illnesses. Although a fever signals that a battle might be going on in the body, the fever is fighting for, not against the person.
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 (40.6°C) unless the child is overdressed or in a hot place.
Febrile seizures do occur in some children. Most febrile seizures are over quickly and do not mean your child has epilepsy. These seizures also 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, including:
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 (37.8°C).
Autoimmune or inflammatory disorders may also cause fevers. Some examples are:
The first symptom of a cancer may be a fever. This is particularly true of Hodgkin disease, non-Hodgkin lymphoma, and leukemia.
Other possible causes of fever include:
A simple cold or other viral infection can sometimes cause a high fever (102°F to 104°F or 38.9°C to 40°C). This does not mean you or your child has a serious problem. Some serious infections don't cause a fever or can cause a very low body temperature, most often 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:
When to Contact a Medical Professional
Call a provider right away if your child:
Call your provider right away if you are an adult and you:
Call 911 if you or your child has a fever and:
What to Expect at Your Office Visit
Your provider will perform a physical exam. This 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 other symptoms.
The following tests may be performed:
Leggett JE. Approach to fever or suspected infection in the normal host. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 280.
Nield LS, Kamat D. Fever. In: Kliegman RM, Stanton BF, St. Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 176.
Section on Clinical Pharmacology and Therapeutics; Committee on Drugs, Sullivan JE, Farrar HC. Fever and antipyretic use in children. Pediatrics. 2011;127(3):580-587. PMID: 21357332 www.ncbi.nlm.nih.gov/pubmed/21357332.
Review Date: 8/5/2018
Reviewed By: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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