Thermoregulation can be described as the processesinvolved in maintaining the core body temperature(CBT) at an optimal level for physiological functioning.The processes can be divided into behavioral thermoregulationand autonomic regulation. The vast majorityof these processes are involuntary and unconscious.The thermoregulatory system controls the behaviornecessary to optimize body temperature, as well as theproduction, conservation and radiation of heat withinand from the body. In a finely balanced system, maintainingthe homeostasis requires constant measurementand adjustment to keep the CBT within minimaldeviations from the optimal level in humans close to3rC, depending on the time of day. These processescan be likened to those of a thermostat, where adjustmentsare made in the way the body either loses orproduces heat to maintain a set point. In the 1950's Aschoff1identified that this finely tuned system was madeup of a core and a shell. The model describes a core orcentral zone in which the temperature is maintained ata very stable 37°C. In contrast, the temperature of theshell varies over a much wider range of temperatures.At the extremities (hands and feet) the skin temperatureis usually considerably lower than the CBT.