what causes fever

Fever is caused mainly by infections such as bacterial, viral, or fungal infections. The body's immune system responds to these infections by raising the body's temperature to help fight off invading germs. This increase is regulated by the hypothalamus in the brain, which raises the body's temperature set point in response to substances called pyrogens released during infection or inflammation. Other causes of fever include inflammatory conditions like rheumatoid arthritis, autoimmune diseases, certain cancers, reactions to medications, heat exhaustion, and vaccinations. The fever occurs because the hypothalamus triggers heat-generating processes (like shivering) and reduces heat loss (by constricting blood vessels) to raise the body temperature to a new set point, making the environment less favorable to pathogens.