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Causes
By Mayo Clinic staffYour normal body temperature varies throughout the day — it's lower in the morning and higher in the late afternoon and evening. In fact, your normal temperature can range from about 97 F (36.1 C) to 99 F (37.2 C). Although most people consider 98.6 F (37 C) normal, your temperature may vary by a degree or more. Other factors, such as your menstrual cycle or heavy exercise, can affect your temperature.
A fever might be caused by:
- A virus
- A bacterial infection
- Heat exhaustion
- Extreme sunburn
- Certain inflammatory conditions such as rheumatoid arthritis — inflammation of the lining of your joints (synovium)
- A malignant tumor
- Some medications, such as antibiotics and drugs used to treat high blood pressure or seizures
- Some immunizations, such as the diphtheria, tetanus and acellular pertussis (DTaP) or pneumococcal vaccines
Sometimes it's not possible to identify the cause of a fever. If you have a temperature of 101 F (38.3 C) or higher for more than three weeks and your doctor isn't able to find the cause after extensive evaluation, the diagnosis may be fever of unknown origin.
- Dinarello CA, et al. Fever and hyperthermia. In: Fauci AS, et al. Harrison's Online. 17th ed. New York, N.Y.: The McGraw-Hill Companies; 2008. http://www.accessmedicine.com/content.aspx?aid=2871330. Accessed April 28, 2011.
- Fever. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/sec14/ch167/ch167e.html. Accessed April 28, 2011.
- Torpy J. Fever in infants. Journal of the American Medical Association. 2004;291:1284.
- Fever, sweats and hot flashes. National Cancer Institute. http://www.cancer.gov/cancertopics/pdq/supportivecare/fever/healthprofessional. Accessed April 28, 2011.
- Febrile seizures fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/febrile_seizures/detail_febrile_seizures.htm. Accessed April 28, 2011.
- Ward MA. Pathophysiology and treatment of fever in infants and children. http://www.uptodate.com/home/index.html. Accessed April 25, 2011.
- O'Grady N, et al. Guidelines for evaluation of new fever in critically ill adult patients: 2008 update from the American College of Critical Care Medicine and the Infectious Diseases Society of America. Critical Care Medicine, 2008;36:1330.
- Sullivan JE, et al. Clinical report — Fever and antipyretic use in children. Pediatrics. 2011;127:580.
- Leggett J. Approach to fever or suspected infection in the normal host. In: Goldman L, et al. Cecil Medicine. 23rd ed. Philadelphia, Pa.: Saunders Elsevier; 2008. http://www.mdconsult.com/books/linkTo?type=bookPage&isbn=978-1-4160-2805-5&eid=4-u1.0-B978-1-4160-2805-5..50307-4. Accessed May 2, 2011.
- Bor DH. Approach to the adult with fever of unknown origin. http://www.uptodate.com/home/index.html. Accessed April 25, 2011.
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