Last reviewed 01/2018

A fever, or pyrexia, is strictly an elevation of body temperature above a normal level e.g. the average core temperature of 37 degrees centigrade. In layman terms, it has become wrongly associated with a clinical syndrome of elevated temperature, chills, shivering, piloerection, vasoconstriction and malaise which is usually followed by vasodilatation and sweating. The latter picture is commonly associated with infective illness.

However, fever is taken as its original definition in this text. This permits the classification of fever in a wider range of conditions such as anterior hypothalamic lesions and with heat stoke.

Fever may be an evolutionary adaptation to infection. It is associated with an increase in antibody production and decreased bacterial division. It is also seen in other mammals, birds, reptiles and amphibia.

Excessive fever, hyperpyrexia, may have a number of causes ranging from over-exercise to extreme sun exposure. Malignant hyperpyrexia is an interesting subtype. Heat stroke is a dangerous complication of hyperpyrexia.