Why Do We Get Fevers?

Fever is not a malfunction but an evolved immune response. When immune cells (macrophages, monocytes) encounter pathogens, they release signalling molecules called endogenous pyrogens (primarily interleukin-1, interleukin-6, and TNF-alpha). These travel through the bloodstream to the hypothalamus (the brain thermostat), which raises the temperature set point. The body then generates heat through shivering, reduced blood flow to the skin (feeling cold), and increased metabolic rate. A higher body temperature benefits the host in several ways: it speeds up immune cell activity, increases antibody production, makes iron less available to bacteria (which need iron to reproduce), and directly inhibits the growth of many pathogens, which are often adapted to 37 degrees Celsius. Most fevers resolve within 1-3 days as the infection is controlled. Fever above 40 degrees Celsius can become dangerous, and above 42 degrees Celsius can cause brain damage and death.