Fever is an important part of the body's defense against infection. Most bacteria and viruses that cause infections in humans thrive best at 98.6°F. Raising the body temperature a few degrees can help the body fight the infection. In addition, a fever activates the body's immune system to make more white blood cells, antibodies, and other infection-fighting agents.
Update Date 8/30/2014
Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.