Mounting evidence suggests that fever may be a strategy for the body to ramp up its defenses. This new understanding could help us develop better approaches to fighting infection altogether.

The hypothalamus controls the body temperature by releasing hormones that cause various heat-boosting responses. The skin′s blood vessels constrict to minimize heat loss from the body′s surface. Fat cells burn energy, and the muscles contract rapidly, causing shivering, ultimately warming up the body and raising the body′s temperature.

A rise too far, however, may be fatal. The cells begin to die, releasing proteins into the blood that can damage the kidneys and other organs, resulting in their failure. This temperature depends on the source of the fever and the person′s hydration status. Fever is associated with a higher pulse and breathing rate, which could be risky in seriously ill people (with heart and lung diseases).

People with infections and a slightly raised temperature tend to recover better than those with a normal temperature or one higher than 40°C, probably because the bacteria and viruses may easily replicate and infect cells at temperatures below 37°C. The immune system also seems to work more efficiently when the body gets hotter.

A recent study suggests that running a temperature of 40°C may help T-cells migrate toward sites of infection from blood vessels by producing proteins that facilitate their anchorage to the blood vessel wall.

Raising body temperature by just a few degrees also speeds up a cellular "clock" that controls a set of inflammation-promoting genes. However, a high temperature can be a response to various problems, like brain injury, heatstroke, and taking certain drugs such as ecstasy.

Most health services advise that a mild fever of up to 38.9°C, in the absence of more worrying symptoms, will resolve with rest and fluids. Thus, when the fever is mild, without any great discomfort, it might remind us what is happening inside the body. 

Geddes L. The fever paradox. New Sci. 2020 Apr 11;246(3277):39-41. doi: 10.1016/S0262-4079(20)30731-4. Epub 2020 Apr 10. PMID: 32372807; PMCID: PMC7195085.