This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
It has just been noted that alcohol produces a relaxation or dilatation of the bloodvessels which ramify through the skin. The dilatation is due to the alcohol causing a slight paralysis of the nerves which control the size of the blood-vessels, thus allowing them to distend a little. A consequence of this is that the general body temperature is lowered. More blood reaches the surface of the body, and more heat is radiated or conducted away. Any feeling of warmth experienced after drinking alcohol is explained by the fact that this flow of blood to the surface warms the skin and the ends of the sensory nerves in the skin, and these convey to the brain a sensation of warmth. But the sensation is illusory; the body as a whole has not really been made warmer.
The fact that alcohol actually lowers the temperature of the body was first announced by Sir B. Ward Richardson in 1866 to the British Association. His observations showed a fall of temperature ranging from three-quarters of a degree (F.) to 3 degrees, the depression persisting not merely for minutes or hours, but even for days. Various observers have since found that ordinary quantities of alcohol taken as a beverage depress the temperature of the body, usually by less than half a degree in healthy men; but large doses may cause a fall of five or six degrees.
The increased loss of heat at the periphery of the body is therefore not compensated by any increased production of heat internally. There is, in fact, no evidence to show that alcohol has any special effect in directly increasing the rate of heat-production in the body, though indirectly it may do this to a small extent - namely, in so far as it favours muscular restlessness by weakening the control exercised by the brain.
The popular belief in alcohol as being a good thing to take in order to "keep out the cold" does not, therefore, appear to have much justification. No doubt to a normal healthy person, well clad, and exposed to a moderate degree of cold for only a short period, the discomfort of chilliness may be alleviated by a small quantity of alcohol without risk of incurring a dangerous fall of internal temperature. But to take alcohol in quantity when the exposure is likely to be prolonged or the cold considerable may be decidedly dangerous, and all the more so because any sensation of warmth which may be produced masks the perception of the real effect, which is a general cooling of the body.
On the other hand, alcohol may be of distinct value after the body has been chilled by exposure to cold such as an immersion in cold water. When the patient has been wrapped in hot blankets, the administration of alcohol is useful, since the liquid, by promoting the return of blood to the surface, can now assist in the absorption of external heat and thus help to restore the general body temperature.