<unk>  Areas that are usually affected include cheeks, ears, nose and fingers and toes.<unk>  is often preceded by frostnip. The symptoms of<unk>  progress with prolonged exposure to cold. Historically,<unk>  has been classified by degrees according to skin and sensation changes, similar to burn classifications. However, the degrees do not correspond to the amount of long term damage. A simplification of this system of classification is superficial (first or second degree) or deep injury (third or fourth degree). First degree * First degree<unk>  is superficial, surface skin damage that is usually not permanent. * Early on, the primary symptom is loss of feeling in the skin. In the affected areas, the skin is numb, and possibly swollen, with a reddened border. * In the weeks after injury, the skin's surface may slough off. Second degree * In second degree<unk> , the skin develops clear blisters early on, and the skin's surface hardens. * In the weeks after injury, this hardened, blistered skin dries, blackens, and peels. * At this stage, lasting cold sensitivity and numbness can develop. Third degree * In third degree<unk> , the layers of tissue below the skin freeze. * Symptoms include blood blisters and "blue-grey discoloration of the skin". * In the weeks after injury, pain persists and a blackened crust (eschar) develops. * There can be longterm ulceration and damage to growth plates. Fourth degree<unk>  12 days later * In fourth degree<unk> , structures below the skin are involved like muscles, tendon, and bone. * Early symptoms include a colorless appearance of the skin, a hard texture, and painless rewarming. * Later, the skin becomes black and mummified. The amount of permanent damage can take one month or more to determine. Autoamputation can occur after two months.Fourth degree<unk>  in a homeless patient five days after freezing conditions. Patient developed trench foot and was unable to properly dry feet.Palmar surface of<unk> en feet five days after a freeze. Patient was homeless with poor footwear.
Frostbite
Chilblains
Crossbite
Trench foot
Overbite
Snakebite
Abrasion 
Nasal fracture