Skin without cold damage (1) has no change in color or texture. Frostnip (2) is the early stage of frostbite. It causes a slight change in skin color and a cold feeling followed by numbness. Frostnip doesn't injure the skin and can be treated with first aid. With superficial frostbite (3), the skin feels warm. A fluid-filled blister may form 12 to 36 hours after rewarming. With deep frostbite (4), skin changes worsen and large blisters may appear 24 to 48 hours after rewarming. Tissue may turn black and hard as it dies.