In this excerpt from his thesis, Dr Ramesh Manocha discusses the physiology of skin temperature:
Unlike the understanding of the ANS and the physiology of the fight or flight response the physiology of human cutaneous circulation is less well understood. Charkoudian (2003) explains that the human cutaneous circulation is controlled by both sympathetic (adrenergic) vasoconstrictor nerves and sympathetic vasodilator nerves. The sympathetic vasodilator nerves are not active in normothermia but are active during exercise, environmental heat exposure and other causes of increased internal temperature. The vasoconstrictor system however, is tonically active even in thermoneutral environments. The vasoconstrictor nerves innervate arteriovenous anastomoses (AVAs) whose highly variable diameter can effectively regulate blood flow to the skin and hence change skin temperature. Small changes in skin blood flow (say, less than 10% of resting neutral levels) mediated by the vasoconstrictor system can lead to substantial increases in rate of heat transfer to the environment. Subtle changes in skin blood flow rates can thereby provide moment-to-moment maintenance of body temperature.