The average body temperature is about 98.6 degrees Fahrenheit. Sometimes your body temperature rises due to exercise, a warm bath, or other factors. Your body will also raise its temperature when it needs to fight infection. High fevers can be caused by illness such as the flu or pneumonia and usually return to normal temperature in a short time. Follow the links below to find WebMD's comprehensive coverage about how a fever is contracted, how to treat it, and more.