Tissue damage caused by extreme cold. Although frostbite is most likely to occur in extremeties (toes, fingers, noses, etc.) because they tend to receive less
blood in cold conditions, frostbite can harm any part of the body that is left exposed. A good way to prevent frosbite in exposed areas like the face is to keep the skin and muscles constantly moving, thereby increasing blood flow and warmth. The colder it is, the faster frostbite takes effect.
Symptoms: The very first symptom is a pins and needles sensation, much like the feeling that your foot is falling asleep. Numbness soon sets in. The skin appears white, cold, and hard to the touch, and then becomes red and swollen. If the frostbite is severe enough to actually kill the skin's underlying blood vessels, gangrene can set in. After thawing, the areas where the tissue is dead will become black, indicating that the damage is permanent. Amputation may be necesssary.
Treatment: Thawing can be attempted only if there is no risk of further freezing. The damaged parts should be warmed as quickly as possible by immersing them in water of about 40 degrees Celsius (hot but not burning). Movement and massage are not helpful. If warm water is not available, cover the area with warm hands or clothing, but never use direct heat.
With information from The Canadian Medical Association Home Medical Encyclopedia