Fever occurs when an area in your brain called the hypothalamus (hi-poe-THAL-uh-muhs) — also known as your body's "thermostat" — shifts the set point of your normal body temperature upward. When this happens, you may feel chilled and add layers of clothing or wrap up in a blanket, or you may shiver to generate more body heat, eventually resulting in an elevated body temperature.
Normal body temperature varies throughout the day — it's lower in the morning and higher in the late afternoon and evening. Although most people consider 98.6 F (37 C) normal, your body temperature can vary by a degree or more — from about 97 F (36.1 C) to 99 F (37.2 C) — and still be considered normal. Factors such as your menstrual cycle or heavy exercise can affect your temperature.
Fever or elevated body temperature 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 vaccine
Sometimes the cause of a fever can't be identified. 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.
May 29, 2014
- Longo DL, et al. Harrison's Online. 18th ed. New York, N.Y.: The McGraw-Hill Companies; 2012. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=4. Accessed Feb. 4, 2014.
- What to do in a medical emergency: Fever. American College of Emergency Physicians. http://www.emergencycareforyou.org/EmergencyManual/WhatToDoInMedicalEmergency/Default.aspx?id=242. Accessed Feb. 17, 2014.
- Fever. The Merck Manuals: The Merck Manual for Health care Professionals. http://www.merckmanuals.com/professional/sec14/ch167/ch167e.html. Accessed Feb. 4, 2014.
- Fever and your child. American Academy of Pediatrics. http://patiented.aap.org/content.aspx?aid=5107. Accessed Feb. 17, 2014.
- Schmitt BD. Pediatric Telephone Protocols. 14th ed. Elk Grove Village, Ill.: American Academy of Pediatrics; 2013:120-124.
- Goldman L, et al. Goldman's Cecil Medicine. 24th ed. Philadelphia, Pa.: Saunders Elsevier; 2012. http://www.clinicalkey.com. Accessed Feb. 4, 2014.
- Wing R, et al. Fever in the pediatric patient. Emergency Medicine Clinics of North America. 2013;31:1073.
- Ward MA. Fever in infants and children: Pathophysiology and management. http://www.uptodate.com/home. Accessed Feb. 4, 2014.
- Febrile seizures fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/febrile_seizures/detail_febrile_seizures.htm. Accessed Feb. 4, 2014.
- Laptook AR, et al. Admission temperature of low birth weight infants: Predictors and associated morbidities. Pediatrics. 2007;119:e643.
- Fever in adults. The Merck Manuals: Home Edition for Patients and Caregivers. http://www.merckmanuals.com/home/infections/biology_of_infectious_disease/fever_in_adults.html. Feb. 25, 2014.
- Hoecker JL (expert opinion). Mayo Clinic, Rochester, Minn. March 4, 2014.