Thermoregulation occurs in the cells of the body as well as for the whole body. A cold cell will have an impaired function when compared with one at optimum temperature and if it freezes, it will suffer irreversible damage internally as well as to the cell wall. Physiological thermoregulation involves methods to increase metabolic heat production as well as to preserve heat loss to the environment mainly by reducing heat (blood) flow to the skin and hence lowering skin temperature. The system of psycho-physiological thermoregulation in cold environments is part of a more complete system for hot, neutral and cold environments (includes vasodilation, sweating, etc.). Although thermoregulation must take place at the level of the cell and is the integrated and interactive system across the body, it is represented as a cybernetic whole-body feedback system and a description can enter at any point.