Frostbite occurs when tissues freeze. This condition happens when you are exposed to temperatures below the freezing point of skin.
The condition has long been recognized. A 5000-year-old pre-Columbian mummy discovered in the Chilean mountains offers the earliest documented evidence of frostbite. More recently, Napoleon’s surgeon general, Baron Dominique Larrey, provided the first description of the mechanisms of frostbite in 1812, during his army’s retreat from Moscow. He also noted the harmful effects of the freeze-thaw-freeze cycle endured by soldiers who would warm their frozen hands and feet over the campfire at night only to refreeze those same parts by the next morning.
Although frostbite used to be a military problem, it is now a civilian one as well. Most people who get frostbite are males aged 30-49 years. The nose, cheeks, ears, fingers, and toes (your extremities) are most commonly affected. Everyone is susceptible, even people who have been living in cold climates for most of their lives.
Your body works to stay alive first and to stay functioning second.
In conditions of prolonged cold exposure, your body sends signals to the blood vessels in your arms and legs telling them to constrict (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.
As this process continues and your extremities (the parts farthest from your heart) become colder and colder, a condition called the hunter’s response is initiated. Your blood vessels are dilated (widened) for a period of time and then constricted again. Periods of dilatation are cycled with times of constriction in order to preserve as much function in your extremities as possible. However, when your brain senses that you are in danger of hypothermia (when your body temperature drops significantly below 98.6°F), it permanently constricts these blood vessels in order to prevent them from returning cold blood to the internal organs. When this happens, frostbite has begun.
Frostbite is caused by 2 different means: cell death at the time of exposure and further cell deterioration and death because of a lack of oxygen.
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. This injury is the primary determinant of the amount of tissue damage you will have in the end.
It is rare for the inside of the cells themselves to be frozen. This phenomenon is only seen in very rapid freezing injuries, such as those produced by frozen metals.