Bacterial infection can also cause the body temperature to rise. In fact, it's one of the most common causes of increased body temperature. Since viruses and bacteria have a hard time surviving at temperatures higher than normal body temperature, when the body detects a bacterial infection, it involuntarily increases its temperature (fever) and increases blood flow to speed up the body's defense actions in order to fight the infection. It's not uncommon for the body to raise its body temperature as much as 3 to 5°F to fight off an infection. Because elevated body temperature also causes harm to the body, we don't want to let prolonged high temperatures go untreated. As we mentioned earlier, isn't uncommon, however, for body temperatures to fluctuate 1° F above or below the normal range. This is considered normal.