In conditions of prolonged cold exposure, your body sends signals to the blood vessels in your arms and legs telling them to constrict or narrow. By slowing blood flow to the skin, your body is able to send more blood to the vital organs, supplying them with critical nutrients, while also preventing a further decrease in internal body temperature by exposing less blood to the outside cold. Periods of dilatation are cycled with times of constriction in order to preserve as much function in your extremities as possible. When this happens, frostbite has begun. In the first, ice crystals form in the space outside of the cells.
Water is lost from the cell s interior, and dehydration promotes the destruction of the cell.
In the second, the damaged lining of the blood vessels is the main culprit. As blood flow returns to the extremities upon rewarming, it finds that the blood vessels themselves are injured, also by the cold. Holes appear in vessel walls and blood leaks out into the tissues. Flow is impeded and turbulent, and small clots form in the smallest vessels of the extremities. Because of these blood flow problems, complicated interactions occur, and inflammation causes further tissue damage.