Stages of frostbite

Skin without cold damage (1) has no change in color or texture. Frostnip (2) is mild frostbite that irritates the skin, causing a change in skin color 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), the skin feels warm. A fluid-filled blister may appear 12 to 36 hours after rewarming the skin. With deep frostbite (4), you may experience numbness. Joints or muscles may stop working. Large blisters form 24 to 48 hours after rewarming. The tissue turns black and hard as it dies.

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