Winter Harm: Cold Dangers

Cold can harm in subtle and quick ways, so it pays to be prepared.
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Cold can harm in subtle and quick ways, so it pays to be prepared.

I had only myself to blame. After a beautiful day of snowshoeing on Red Mountain Pass near Ouray, Colorado, I felt awful. By the time we returned to the car, the underside of my nose was sunburned, my skin was cold and clammy with sweat, and my shoulders were cramped from hunching them against the wind biting through my fleece. To add insult to injury, my husband kept making jokes about my chattering teeth.

Luckily this was just a day outing; if it had been an overnight excursion, my poor cold-weather management could have put me in serious trouble. The good news is that such winter consequences are easily avoided once you understand how cold affects your body.

Frigid, blustery, wet winter weather robs your body of precious heat four sneaky ways: through radiation, conduction, convection, and evaporation.

Radiation

In a house, radiators get hot and warm the air around them. Insulated walls hold in the heat and prevent the warm air from drifting off into the cold night. In the backcountry, appropriate clothing (see "Conduction" below for examples) and a good sleeping bag hold in the heat produced by your body. Just remember, if you wear the wrong kind of clothing or expose your skin, you'll lose more heat through radiation as the temperature drops.

Radiation beater: Use your head. You've probably heard that up to 70 percent of your body heat can be lost through an uncovered noggin. While this of course depends on lots of variables, including your hairline and the clothing you're wearing, the point is worth stressing. The scalp is well supplied with lots of heat-shedding blood vessels, and it lacks insulating layers of fat to keep that heat inside. The bottom line: Put on a hat when you start to feel chilled. Rick Curtis, director of the Outdoor Education Program at Princeton University and author of Backpacker's Field Manual: A Comprehensive Guide to Mastering Backcountry Skills (1998; Three Rivers Press, 1-800-733-3000; $14.95) suggests choosing one with "idiot strings" that tie under the neck. "If you overheat, push it off your head and leave it tied so it won't blow away or get lost," he recommends.

Conduction

This one occurs when your body contacts something that's colder than you are, like when you wrap your hands around an icy water bottle or fuel canister. The result is that the object immediately sucks heat from your body. Conduction normally accounts for about 2 percent of overall heat loss. Since water conducts heat much more efficiently than air does, wet clothes can bleed your body's warmth up to 25 times faster than if those same clothes were dry.

Conduction beater: "Anticipate sweat production," says Murray Hamlet, director of research plans and operations for the Army Research Institute for Environmental Medicine in Natick, Massachusetts. "If you know you'll be hiking uphill, take off some clothes before you start. Keep your skin a little cold all the time (while moving)." The key is layering: a hydrophobic (water-hating) inner layer, an insulation layer or two, plus a windproof outer layer. "Look for clothes with zippers," adds Curtis, "so you can vent to prevent perspiration."

To maintain dry feet, Hamlet recommends antiperspirant. "Apply it three times a day for a week (before a trip), then once or twice a day" while backpacking. And even though we've said it before, it bears repeating: Shun cotton-it's a water-retaining heat-drainer. Stick with synthetics or wool for winter wear.

Convection

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.

Evaporation

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.

Furnace Stoking

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.