In cold-weather folklore, the flask of whiskey is standard equipment. Stranded in a blizzard? Brandy warms you from the inside. The Saint Bernard carries a barrel of it for a reason.

Excerpted from You’re Doing It Wrong

It is one of the most pervasive images in film: taking a shot of something while cold. It is also dead wrong.

Alcohol creates the sensation of warmth. It does not create warmth. And in a genuine cold-weather survival situation, this distinction can be fatal.

What alcohol does is dilate peripheral blood vessels — the small blood vessels near the skin’s surface. This increased blood flow to the skin produces a flushing sensation: warmth spreading through the face, hands, and extremities. The perception is real. The physiology is the opposite of helpful.

Your core body temperature is maintained by keeping warm blood in the body’s core — heart, lungs, vital organs. When cold threatens, blood vessels near the skin constrict, routing blood away from the surface and back toward the core to preserve heat where it matters. Alcohol reverses this process: it dilates peripheral vessels and moves warm blood toward the surface, where it loses heat to the environment rapidly.

The result: the skin feels warm. The core temperature drops. The sensation of cold may actually diminish as the core cools, because alcohol also impairs thermoregulatory sensation. A person who has been drinking in cold weather may feel warm and comfortable while their core temperature is actually declining. This is the mechanism by which alcohol contributes to hypothermia deaths: people don’t feel cold enough to take protective action.

Over the centuries, many a drunk has been found frozen to death.

In survival medicine, alcohol consumption in cold environments is a specific risk factor for hypothermia, not a protection against it. The Saint Bernard’s barrel is picturesque. It is also bad survival medicine. The flask in the blizzard kit does not belong there.

I cover all the proper procedures for cold weather operations (I was in the Special Forces Group that was oriented toward mountain and cold weather operations and we conducted Winter Warfare training every year when possible) in my Preparation and Survival Guide.