A rise in body temperature is often the first obvious sign that something is wrong. Fever is an elevation of core body temperature above the normal range, usually defined as 38°C or higher, produced by the immune system’s response to infection or other inflammation.

Pyrogens reset the hypothalamic thermostat, generating heat through shivering and reduced heat loss. Mild fever may aid host defense; high fever can cause discomfort and, in susceptible people, seizures or metabolic stress. Associated symptoms and the clinical context determine whether investigation and treatment are needed.

Antipyretics such as acetaminophen lower temperature and improve comfort but do not treat the underlying cause. Persistent or extreme fever, or fever in immunocompromised patients, warrants prompt medical evaluation. Temperature measurement technique affects accuracy and should be standardized.

• Elevated core body temperature from immune activation
• Commonly defined as 38°C or above
• Usually a response to infection or inflammation
• Treated for comfort while the cause is addressed