Normal body temperature changes during the day. Exercise, stress , or dehydration may cause a person's temperature to go up. In these cases, it is not considered a true fever. Fever is a symptom, not a disease. A fever may mean that there is something else going on in the body that is causing it.
Fever helps the body fight infections by making the body's defense systems work more efficiently.
Bacteria and viruses cannot live at higher temperatures and so are killed by fever. The signs and symptoms of a fever depends on what is causing it. At first, a fever can cause a chill. Shivering produces heat in the body. Once the temperature goes up, the person often feels warm.