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Frostnip is a superficial nonfreezing injury causing local paresthesias of the involved area that completely resolves with passive external rewarming. It is distinct from frostbite in that ice crystals form on the skin but not within tissues and no tissue loss occurs. Rewarming can be done by placing cold fingers in the axilla and in the case of the toes or heels, by removing footwear, drying feet, rewarming, and covering with adequate dry socks or other protective footwear.
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Chilblains, or erythema pernio, are inflammatory skin changes caused by exposure to cold without actual freezing of the tissues. These skin lesions may be red or purple papular lesions, which are painful or pruritic, with burning or paresthesias. They may be associated with edema or blistering and aggravated by warmth. With continued exposure, ulcerative or hemorrhagic lesions may appear and progress to scarring, fibrosis, and atrophy. This may resemble vasculitis or peripheral thromboemboli. A detailed history of cold exposure will differentiate chilblains from other conditions, thereby avoiding unnecessary diagnostic testing. Chilblain lupus erythematosus, while clinically similar to ordinary chilblains, can be differentiated by an association with other lupus manifestations or by biopsy. Treatment consists of elevating and passively externally rewarming the affected part.