Fever describes the situation of an elevated thermostat set point in the hypothalamus followed by an increase in body temperature maintained at the higher level. Pyrogens are the compounds that are able to increase the thermostat set point. Fevers have diverse causes:
- clinical problems that restrict blood flow at the level of the hypothalamus
- conditions that impair sweat gland activity (certain drugs)
- abnormalities affecting the thermoregulatory centre (e.g. brain tumors)
The reaction of the body against an infection involves fever. This fever costs an individual more fluids, but no extra calories.
Fever is such a reliable indicator of the presence of disease, that body temperature is the most measured clinical index.
Within a few hours after the thermostat setpoint has been set to a higher level, the body temperature will approach this level.