Frostbite is damage to your body's tissues caused by freezing. When skin and the flesh underneath get cold enough to actually freeze, ice crystals form inside the cells and can destroy them. This most often happens to body parts farthest from your heart: fingers, toes, ears, nose, and cheeks.

Frostbite usually starts with a pins-and-needles feeling, then the affected area goes numb and turns pale or grayish. In severe cases, the frozen tissue can die and turn black. Mountain climbers on peaks like Everest risk frostbite in the extreme cold, which is why they wear so many layers and cover every bit of exposed skin. Even in less extreme conditions, like playing outside on a very cold winter day with wet gloves, you can get mild frostbite if you stay out too long.

Body parts badly damaged by frostbite may need to be amputated. This happened to some of the early polar explorers who pushed too far into frozen territories. Today we know that the key to preventing frostbite is keeping your extremities warm and dry, limiting time in extreme cold, and coming inside at the first sign of numbness.