Frostbite

Frostbite is a freezing injury, most often affecting fingers, toes, ears, nose, and other exposed areas with limited blood flow. Cold first causes vasoconstriction, reducing heat loss but also reducing tissue perfusion. When tissue temperature falls below freezing, ice crystals form within and around cells. The crystals disrupt cell membranes, pull water out of cells, and alter electrolyte balance. The visible injury may worsen after the person is warm. Rewarming restores blood flow to damaged vessels, but injured endothelium promotes leakage, platelet aggregation, and microvascular thrombosis. This is why a digit can look relatively intact before thawing yet become swollen, blistered, dusky, and painful afterward. The damage is not determined by skin colour alone; it reflects both freezing and the vascular injury that follows. A partially thawed extremity that freezes again sustains much more damage. If safe shelter is unavailable and refreezing cannot be prevented, protect the part from further cold and trauma while arranging evacuation rather than allowing repeated thaw-freeze cycles.