Frostbite is damage to the skin and other tissues caused by freezing. Frostnip is a mild form of cold injury. In North America, frostbite is largely confined to Alaska, Canada, and the northern states. Recently, there has been a substantial decline in the number of cases and a change in the type of people at-risk, as outdoor winter activities have grown more popular and there are more homeless people. Exposure to temperatures a little below the freezing mark can take hours for skin to freeze, but very cold skin can freeze in minutes or seconds. Air temperature, wind speed, and moisture all affect how cold the skin becomes. The extent of permanent injury depends upon how long the skin and tissues remain frozen. Homeless people and others lacking strong self-preservation instincts face a greater risk of frostbite-related amputation because they are more likely to...