What causes a fever?
Fever is the result of an immune response by your body to a foreign invader. These foreign invaders include viruses, bacteria, fungi, drugs, or other toxins.
These foreign invaders are considered fever-producing substances (called pyrogens), which trigger the body's immune response. Pyrogens signal the hypothalamus in the brain to increase the body temperature set point in order to help the body fight off the infection.
Fever is a common symptom of most infections such a colds and gastroenteritis (also referred to as stomach flu), and thus a risk factor for fever is exposure to infectious agents. Typical infections that may cause a fever include those of the ear, throat, lung, bladder, and kidney. In children, immunizations (such as vaccine shots) or teething may cause short-term low-grade fever. Autoimmune disorders (including rheumatoid arthritis, lupus, and inflammatory bowel disease), medication side effects, seizures, blood clots, hormone disorders, cancers, and illicit drug use may also cause fevers.
Fever itself is not contagious; however, if the fever is caused by a viral or bacterial infection, the infection may be contagious.