Cold air on bare skin is uncomfortable. Severe cold on bare skin can be dangerous in a way most people don’t fully appreciate. When skin freezes - actually freezes, with ice crystals forming inside the cells - the result is called frostbite, and it can permanently destroy tissue.
Frostbite happens when skin temperature drops below 31°F (-0.55°C). Ice crystals start to form between cells, then inside them. The crystals tear the cells apart from within. Blood vessels constrict to try to preserve heat for the body’s core, cutting off blood flow to the frozen tissue. Without blood, the affected cells start dying.
The most vulnerable parts are the extremities: fingers, toes, nose, ears. They have lots of surface area, less insulation, and farther from the body’s warm core. In extreme cold with wind chill, exposed skin can frostbite in just 5-10 minutes. Mild frostbite (“frostnip”) usually fully recovers. Severe frostbite can kill the tissue completely, leading to amputation in some cases. The classic treatment for early frostbite is to slowly warm the affected area with warm (not hot) water - rapid heating can cause more damage. Better still: don’t get frostbite. Wear gloves.
