Frostbite

Frostbite is a medical condition caused by exposing skin to extreme cold. I've mentioned it a few times while writing about cryogenic gasses (anhydrous ammonia and liquid propane gas), so it's not an exclusively a winter-time threat, but during winter exposed areas like fingers, toes, ears, noses, cheeks, and chins are the most commonly affected areas.

Where fire and heat damages tissue like skin by cooking it, frostbite damages it by freezing. If skin gets too cold, the tissue under it will start to freeze, causing the cells to burst as the water that makes up 60-70% of each cell expands. Further damage is caused by the loss of blood flow to the frozen tissue, leading to tissue death (necrosis). This can cause damage ranging from irritation to amputation, similar to burns. Like burns, frostbite has been broken down into three levels or degrees.

Level 1

• Numbness and loss of movement or dexterity
• Skin may also turn red, similar to a 1^st degree burn

Frostnip is the first indication that your exposed skin is too cold, and is also a sign that your extremities have been sensitized to the cold due to previous damage from freezing. I have a few fingers that got frostbite a long time ago, and the nerves in those fingers took some damage. They are the first to go numb or “pins and needles” when exposed to cold now, almost 50 years later.

Treatment is simple: gently warm the cold tissue to restore proper blood flow and keep it warm until normal functions are restored. Placing the affected body part into warm (not hot!) water works well. Hot water won't work because your affected parts won't be able to feel the temperature properly, and if the water is too hot you can cause extra damage. If warm water is not available, add insulation to the affected body part and increase your physical activity to warm it from the inside with increased body temperature and blood flow. As the tissue warms up and nerves are reactivated, you're going to feel a lot of pain. It's going to feel like the affected tissue is on fire and you're going to want to stop the warming. Keep it up until things start to feel normal again.

Level 2

• Skin is hard to the touch and white or waxy looking
• Fingernails and toenails of affected area will no longer show capillary refill 
• Blisters and peeling skin, similar to a 2^nd degree burn, are common 

Frostbite is when the tissue under the skin is frozen solid and needs to be treated ASAP. A blueish tint to the skin is a sign that it has lost blood flow and is not getting enough oxygen.

Capillary refill is a simple check: Press down on the nail -- it will go white as you squeeze the blood out of the capillaries -- then release.  Normal blood flow will return the pink color in less than a second, but reduced or stopped blood flow will cause them to stay white.

Treatment is similar to Level 1, but will take longer and needs to be monitored more closely for signs of necrosis. Hands and feet are easy to warm by placing them under your or another's armpits. Think of the places where you sweat the most, and those are the areas that tend to be the warmest; the armpits and crotch are the easiest to access. Shared body heat can be a medical treatment, so two or more naked people sharing a sleeping bag might not be what you think.

Level 3

• Skin has turned a darker color and is as hard as ice

This is the level that causes people to lose fingers, toes, ear lobes, and parts of their noses in order to save their lives. Once the skin turns dark, it and the tissue underneath it has died and is not going to come back. Dead tissue is a prime breeding ground for bacteria like gangrene, so debridement, or removal of the dead tissue, is the only common treatment.

Treatment at this level requires medical training and equipment, so get the injured person to a hospital. My opinion, and I am NOT a doctor, is that frozen tissue is dead and I wouldn't want to restore blood flow that could pump dead or damaged blood cells back into the rest of the body unless I had antibiotics, blood thinners, and other measures at hand. I'd leave frozen tissue frozen until treatment was available,while keeping other areas from freezing. 

Prevention

Frostbite hits the young and old the hardest because they have a hard time controlling their body temperature. Use of alcohol, tobacco, and a lot of medications that limit blood flow will make you more susceptible to frostbite. Dress in layers, cover your ears, face, and extremities, and keep an eye on your friends and family. It's hard to look at your own ears and face, so you can develop frostbite and not know it until someone else points it out.