Moving air or water snatches the heat from your skin even faster than radiation or conduction. “Wind kills,” says Hamlet. “It removes the layers of the still-warm air in our clothes and whisks away body heat fast.”
Convection beater: Your cozy fleece jacket and pants won’t keep you warm without a windproof layer over them. Even wearing the windproof layer alone will warm you considerably when a breeze kicks up. Also, protect your face and eyes from chapping and windburn with petroleum jelly or a thin layer of diaper rash ointment (zinc oxide), and goggles or wraparound glasses. If the wind is really bad, “find shelter,” Hamlet says.
Even sweating and breathing cause moisture loss through evaporation, which can lead to dehydration any time of year. The risk is particularly high in winter, though, because people aren’t as aware of their fluid needs during cold weather. When you don’t drink enough, your blood thickens and there isn’t as much moving through your body to keep you warm. Consequently, dehydrated people are more susceptible to cold-injuries, says Howard Donner, MD, a family sports and emergency medicine doctor in Telluride, Colorado, and coauthor of Field Guide to Wilderness Medicine (1998; Mosby-Year Book Inc., 800-426-4545; $34.95). “In an attempt to maintain normal blood pressure for vital organs, your body clamps down on peripheral blood vessels,” which results in cold fingers, toes, ears, and nose. In extreme conditions, it contributes to hypothermia and even frostbite.
Evaporation beater: Drink plenty. “It really doesn’t make a difference what you drink,” Donner says. “You hear you should never drink coffee or tea because they’re diuretics. That’s overstated; it’s just that the return is lower,” so you have to drink that much more. An insulated bottle of warm water or a hot sports drink is better. Curtis recommends drinking 16 ounces of liquid before hiking, then 10 to 12 ounces every 30 minutes during activity.
Once you’ve chinked all the cracks that let body heat escape, you’ll still need to keep the furnace stoked. Here’s where it pays to be fit, but not necessarily thin. “Muscle is where metabolic heat is produced,” Donner says. “The more muscle you’ve got, the more heat you can make.” Spend too much time sitting around not using those muscles, and the body compensates with chattering teeth and shivering. “The metabolic heat energy produced by shivering is huge, almost like jogging, but it’s an inefficient use of energy. Most people can’t shiver for more than 2 hours because their muscles run out of fuel.”
Heat generator: “If you start to chill, increase your activity level,” recommends Curtis. “The best thing to do is jump around, which uses your body’s biggest muscles.” Jumping jacks, jogging in place, anything that engages the big thigh and butt muscles is great. Just don’t overdo it and work up a sweat. Keeping your body well supplied with heat-generating food calories is also a big part of staying warm in the winter.