A fever is often a sign that the body is fighting an illness or infection. It is not a disease itself but a symptom of an underlying issue. Understanding what causes fever can aid in its treatment. Infections are the most common cause of fevers. These include various viral infections like colds, the flu, and COVID-19, as well as bacterial infections such as urinary tract infections and pneumonia. When someone has an infection, their immune system responds by raising the body temperature, resulting in a fever. Fever can also be caused by reactions to medications. In such cases, the body may perceive a drug as a foreign substance, leading to an immune response and resulting in fever. This type of fever usually subsides once you stop taking the medication or your body adjusts to it. Exposure to excessive heat, either from the environment or through extreme physical activity, can also cause fever. This occurs when the body's temperature control mechanisms are overwhelmed, leading to high body temperatures. Other factors that can cause fevers include allergic reactions to foods or drugs, heat-related illnesses, and chronic conditions. While most fevers indicate minor illnesses, accompanying symptoms, and overall health status are important in determining the severity and whether medical consultation is necessary.