Frostbite occurs when people are exposed to cold temperatures for extended periods without sufficient protection. Skin and, if exposure is prolonged, deeper tissues, including nerves and blood vessels, can be damaged beyond repair. Frostbite begins at the extremities (fingers, toes, ears, etc.) as the body tries to protect vital organs by constricting blood vessels at the extremities. This moves warm blood toward the center of the body. While this natural adaptation is important for keeping the heart pumping and other organs working, if circulation is cut off too long in other areas, tissues will die.

The first stage of frostbite is frostnip, which is when skin begins to get numb but no damage to the tissues occurs. In first-degree frostbite, ice crystals begin to form on the skin, and a warming sensation in fingers or toes indicates the onset of second-degree frostbite. As the damage progresses to third-degree frostbite, extremities turn blue, white, or red, and in the last stages—fourth-degree—purple and then black. At this advanced stage, sensation is lost as nerves die, and it may be necessary to amputate. The best way to avoid frostbite is to simply stay indoors, especially if the wind chill is –50°F (-45.5°C) or lower. If you must go outside, bundle up, don’t drink alcohol or caffeinated beverages, and also avoid smoking. Drinking and smoking can both constrict blood vessels, thus speeding the formation of frostbite.