Fever and antipyresis.

Whether fever represents a beneficial or harmful response to infection has been debated for hundreds of years. The issue is clouded by a common misunderstanding that fever is the reason an individual with infection feels ill: often once the elevated body temperature abates, the patient feels better. It is assumed therefore that reducing the fever would improve the patient’s condition and shorten their illness. From there, it is only a short step to conceive of the fever as the illness itself. Although this logical fallacy remains attractive to medical personnel and patients, what evidence exists that fever is harmful or beneficial to the course of an infectious illness? At first glance, studies to answer the question seem simple to perform. Unfortunately, however, to investigate the problem directly is virtually impossible, because every method available to reduce fever has secondary metabolic consequences: antipyretics affect the body in many ways, and even physical methods — such as sponging with cold water — result in a wide range of responses, including shivering and stimulation of the adrenal–cortical axis. We thus must seek other lines of evidence — ranging from teleology and comparative zoology through detailed clinical observation of defined cases to molecular biology. Perhaps the most powerful arguments to support a beneficial effect of fever on infection come from teleology and genetics. Fever is established as a phylogenetically ancient host