Cold is a vasoconstrictor, while heat is a vasodilator. In general, these statements hold for skin perfusion. However, the variation in circumstances, between skin sites and between individuals is large. Moreover, the regulation of blood perfusion is complex, making understanding the relation between heat exchange and skin perfusion an appealing task. Approximately 90 % of our heat production is lost via the skin, the body heat mainly transported to the skin by the blood. Therefore, it is remarkable that relatively little attention is given to skin blood flow and its regulation in human physiological metabolic studies and in physiological models of thermoregulation.

Metabolic studies in general measure energy expenditure by means of indirect calorimetry. In a small subset of studies skin and core temperatures are being measured simultaneously, but skin blood flow measurements of different skin types are rarely taken into account.

This overview deals with those studies that combine heat production and heat loss with special attention to individual variation. Studies range from those using direct and indirect calorimetry to those measuring local skin perfusion. The different techniques will be discussed briefly.

Special attention will be given to whole body and local cooling in young compared to elderly and between different skin sites (glabrous versus nonglabrous skin). During cold exposure, a decrease in skin perfusion is the first line of defense in human thermoregulation. Control of skin perfusion is via both central and local mechanisms. Generally both mechanisms act simultaneously. With increase in age there is an attenuation of the cutaneous vasoconstrictor (VC) response to whole body cooling, predisposing the older population to risk of hypothermia. Innervation and topology of cutaneous microcirculation is not homogenous. For instance, glabrous skin (palms, soles, lips) is relatively well adapted for regulating heat loss. Moreover, the hands and the face are the areas of the skin that are actually exposed to the environment, making them the primary heat exchangers of the human body. Therefore, studies will be presented on local and reflex mediated mechanisms of vasoconstriction in whole body and local cooling at glabrous and non-glabrous skin sites in male young adults and elderly.

Finally, we describe a human thermophysiology model in which the regulation of blood perfusion will be incorporated.