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Causes

By Mayo Clinic staff

Your 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.

References
  1. 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.
  2. Fever. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/sec14/ch167/ch167e.html. Accessed April 28, 2011.
  3. Torpy J. Fever in infants. Journal of the American Medical Association. 2004;291:1284.
  4. Fever, sweats and hot flashes. National Cancer Institute. http://www.cancer.gov/cancertopics/pdq/supportivecare/fever/healthprofessional. Accessed April 28, 2011.
  5. 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.
  6. Ward MA. Pathophysiology and treatment of fever in infants and children. http://www.uptodate.com/home/index.html. Accessed April 25, 2011.
  7. 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.
  8. Sullivan JE, et al. Clinical report — Fever and antipyretic use in children. Pediatrics. 2011;127:580.
  9. 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.
  10. Bor DH. Approach to the adult with fever of unknown origin. http://www.uptodate.com/home/index.html. Accessed April 25, 2011.
DS00077 June 1, 2011

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