Fever: Abnormal increase in body temperature. Fever is not always related to an underlying condition. It may be caused by: injury, side effects of drugs, over exertion of the body, pain, stress, teething, vaccine side anuses.xyz about fever. Mar 25, · Treating a fever. Fever is part of your body's defense against infection-causing germs. By itself, fever is usually harmless, though a high fever can be miserable. These steps may help you feel .