Human cold stress is the continuous and dynamic combined interaction of the effects on a person of variables air temperature, radiant temperature, air velocity and humidity, as well as clothing and activity, that can result in a drop in body temperature. ‘Adaptive opportunity’ that ‘allows’ behavioural responses is an important characteristic of the environment and should be a fundamental part of environmental design. It could be regarded as a seventh basic ‘parameter’ and is an essential consideration in any modern assessment of human cold stress. Feeling cold is a consequence of physiological regulation as vasoconstriction ‘attempts’ to preserve heat but lowers skin temperature particularly in the hands and feet. The drive for behavioural response is very strong and taken as a whole provides a framework for the consideration of human cold stress. Feelings of thermal discomfort and physiological responses can be predicted by a calculation based upon the heat transfer between the body and the environmen.