Secrets of winter warmth: avoiding hypothermia, frostnip, and frostbite.

I confess. I'm an avid winter mountaineer. If It's got snow and ice, I'll do it. I remember once it was 10 [degrees] F with a howling wind and I was half dressed in my sleeping bag with one leg hanging out, trying to stay cool. While most people prefer not to saunter around in a sleeping bag, with a few dollars and some cold weather savvy you can be comfy on even the most brutal winter day.

Being cold weather-wise, you know there's a difference between dressing to shovel snow versus hanging out at a local pond watching junior skate. You know that dressing properly not only keeps you from being cold and miserable but also helps prevent nasty cold weather injuries like hypothermia, frostnip, and frostbite.

Jack Frost Has a Nasty Bite

It may be a winter wonderland, but if you don't bring a pair of gloves, you may spend Christmas at the local emergency room instead of relaxing by the fire at Uncle Ed's. Frostnip and its evil cousin frostbite are 100 percent preventable. Frostnip involves only the superficial skin and can be recognized by firm/pale skin. Frostbite can extend to muscle and bone and looks like frostnip except the affected area is white and senseless. Frostnip is very painful. If the area is numb, think frostbite. Frostnip is treated by simply rewarming the affected area. Frostbite is serious and demands medical attention as soon as possible.

As with any injury, prevention is the key. Besides dressing properly, always wear gloves when touching cold metal, which can actually freeze unprotected skin. Also, if your toes and fingers are cold or numb, wiggle them vigorously--this increases blood flow and helps prevent frostbite. Finally, more bad news for smokers: nicotine is a strong vasoconstrictor that decreases circulation to your extremities and promotes frostbite. Smoking is bad for you in more ways than you can imagine. Remember, while the vast majority of frostbitten fingers and toes are saved, don't underestimate frostbite. Go to the emergency room! People have lost frozen limbs and have died from infection.

Winter Stealth: Hypothermia

Hypothermia occurs when body temperature dips below 95 [degrees] F. Though most commonly seen in winter, hypothermia can actually strike anytime, even during the summer, catching its victims off guard.

The tragedy usually begins with a walk in the woods. Someone gets caught in a storm, their wet clothes rob them of body heat, and before they know it, hypothermia sets in.

Besides dressing properly, recognizing hypothermia is key to prevention. Hypothermia begins with uncontrollable shivering as muscles desperately attempt to generate heat. As body temperature falls below 95 [degrees] F, fatigue, incoordination, and confusion set in. At 90 [degrees] F you become comatose. At 80 [degrees] F the heart stops. If you can't stop shivering, keep moving and seek warm shelter immediately.

If your companion acts confused or stumbles continuously, he or she may be hypothermic, and it's critical you find shelter and call a doctor. Don't be fooled by someone who stops shivering this may mean the body is exhausted and has given up. Trust your instincts; if you think something is wrong, it probably is.

An Ounce of Prevention...

Perhaps the real tragedy of cold weather injuries is that they're 100 percent preventable. Prevention starts with my favorite--the stomach. During the winter it's important to be adequately fed and hydrated. In fact, your body can demand more water in the winter than the summer, as your lungs lose moisture humidifying and warming dry, cold winter air. The average person needs about 1.5 to 2.5 liters per day, whereas a winter athlete may require 2.5 to 5 liters per day.

You'll also have to eat more. Most people need about 1,500 to 2,000 calories per day; winter mountaineers, however, may demand 4,000 calories per day. A low-fat diet of 65 percent carbohydrates, 20 percent protein, and 15 percent fat is best. Finally, avoid alcohol. Contrary to popular belief, alcohol cools you down.

Clothing

The First Layer. Two fundamental principles underlie winter warmth. The first is to maintain a layer of warm air between your skin and the environment. When you're adequately fed, your body generates heat. When you're adequately dressed, this heat is trapped by your clothes.

The second principle of winter warmth is to keep moisture off your skin. Moisture robs heat from your body. Clothing should be chosen not only for insulating capacity but also for the ability to resist wind and moisture. Cotton is a great insulator and can be safely worn if you're close to shelter and there's absolutely no chance of getting wet. But wet cotton saps away body heat, and many hypothermic deaths occur when people get caught in a storm while wearing cotton. If you're far from shelter or intend to sweat, or there's a chance you'll get wet, wear fleece (Capilene) undergarments. This fabric is a magnificent insulator that keeps moisture away from your skin and dries fast.

The Second Layer. Wool is king; it not only is fashionable but also repels moisture and insulates when wet. Again, cotton's OK if you're close to home, but potentially deadly when wet. Wool or synthetic pile is mandatory for foul weather or wilderness jaunts. I usually wear a wool shirt followed by a wool sweater. Shirts are superior to pullovers, as button-up shirts allow you to control how much you cover up. Pullovers are an all-or-nothing phenomenon; after rolling up the sleeves, there's little more you can do except sweat or take the garment off.

Wrapping It All Up

Jackets. Choosing a jacket depends a lot on your wallet and expectations. Though I'm partial to down, it's expensive and loses some of its insulating capacity when wet. This means you have to protect down with an expensive waterproof fabric like GoreTex if there's a chance you'll run into foul weather. Gore-Tex is wonderful, both waterproof and windproof.

For cost-conscious consumers, a number of new synthetic insulators like Thinsulate and Primaloft have been developed that are less expensive, insulate when wet, and are less bulky than down. Then there's the question of whether or not to insulate at all. If you're shoveling snow, you don't want lots of insulation making you overheat and sweat.

The feet. There is nothing worse than half-frozen, waterlogged feet. The answer boots. I prefer boots because they permit the foot to breathe. Don't get me wrong--rubber boots are great. It's an aesthetic issue. A good boot will rise above the ankle to provide support during inevitable winter slips and make it difficult for slush to invade your shoe. Inside the boots, use a polypropylene liner to whisk away foot moisture and cover it with one or two pairs of wool socks. Remember, when buying boots bring your anticipated sock arrangement to the store, or your feet may have a tight, uncomfortable winter. Even worse, tight boots encourage frostbite by hampering circulation. Finally, unless you're a runner or live in southern California, mothball the sneakers. They offer zero insulation and no support, and water pours through them.

Mother Knows Best

Remember Mom telling you to put on your hat and gloves? She was on to something. The head and neck receive a tremendous amount of blood and consequently are major areas of heat loss.

Want to be warm? Wear a hat and scarf. The best thing I ever bought was a balaclava: a hat, scarf, and face mask all in one. I love my balaclava, have owned it for 20 years, never will retire it, and still can't pronounce it. If I'm too warm, I roll it into a hat. If I'm too cold, I pull it over my nose, mouth, and neck.

Gloves come in a variety of fabrics ranging from thin silk to fully insulated Gore-Tex body armor. What you wear depends on what you do. When manual dexterity is at a premium (e.g., picture taking), I use a pair of thin cotton gloves. If I want to keep my hands toasty warm, I wear a pair of insulated mittens, which keep the fingers together, happy to share each other's warmth.

Final Word

There is no magic to being warm on even the most brutal winter day. Common sense and sophisticated clothing choices make the difference. Layer your clothes and choose fabrics appropriate for your level of activity and risk of exposure to wet weather. Remember, protect your nose, ears, and fingers, as frostbite loves to attack these areas first. How much you put on depends upon your personal thermostat. When in doubt, overdress; you can always take it off.

Jonathan M. Berkowitz, M.D., is a pathologist and medical writer in New York City.