Frostbite

Frostbite is tissue injury caused by freezing, usually affecting exposed skin and underlying structures. It can progress from reversible damage to cell death and tissue loss.

Ice crystal: A solid crystalline form of water whose structure depends on temperature and pressure. Ice crystals form within and around cells during freezing, disrupting tissue structure.
Cold injury: Tissue damage caused by exposure to cold, including injuries that do not involve freezing. Frostbite is the freezing form of cold injury, distinct from nonfreezing damage.
Freezing point: The temperature at which a liquid changes into a solid under specified conditions. Tissue freezing occurs below the effective freezing point of body fluids.
Chilblains: Inflammatory skin lesions caused by repeated exposure to cold, damp conditions without tissue freezing. Chilblains cause painful or itchy lesions but do not involve the freezing central to frostbite.
Vasoconstriction: The narrowing of blood vessels caused by contraction of their smooth muscle walls. Cold-induced vasoconstriction reduces blood flow to exposed tissues before freezing occurs.
Frostbite classification: A clinical system for grading frostbite severity by tissue depth and likely damage. Grades help describe how far freezing injury extends and estimate tissue loss.
Wind chill: An estimate of how quickly exposed skin loses heat under combined air temperature and wind conditions. Wind accelerates heat loss and can shorten the time before exposed skin freezes.
Trench foot: A nonfreezing cold injury caused by prolonged exposure of the feet to wet, cold conditions. Trench foot can damage tissue without the ice formation that defines frostbite.
Reperfusion injury: Tissue damage caused or worsened when blood supply returns after a period of restricted circulation. Restoring circulation during thawing can trigger inflammation and further tissue damage.
Thrombolysis: The dissolution of blood clots using medication or other interventions. Selected severe frostbite cases may receive clot-dissolving treatment to restore circulation.

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