Stages of frostbite
Skin without cold damage is normal (1). Frostnip (2) is mild frostbite that irritates the skin, causing redness and a cold feeling followed by numbness. Frostnip doesn't permanently damage the skin and can be treated with first-aid measures. With superficial frostbite (3), your skin feels warm, a sign of serious skin involvement. A fluid-filled blister may appear 24 to 36 hours after rewarming the skin. With deep frostbite (4), you may experience numbness. Joints or muscles may no longer work. Large blisters form 24 to 48 hours after rewarming. Afterward, the area turns black and hard as the tissue dies.
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