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Frostbite

Frostbite Overview

Frostbite occurs when tissues freeze. This condition happens when you are exposed to temperatures below the freezing point of skin. Hypothermia is the condition of developing an abnormally low body temperature. Frostbite and hypothermia are both cold-related emergencies.

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. 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. Some groups of people at greatest risk for frostbite and hypothermia include people:

  • who spend a great deal of time outdoors, such as the homeless, hikers, hunters, etc.;

  • under the influence of alcohol;

  • who are elderly without adequate heating, food, and shelter;

  • who are exhausted or excessively dehydrated;

  • who are mentally ill.

Frostbite Causes

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 two 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 that occurs 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.

Picture of the stages of frostbite



Next: Frostbite Symptoms »

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Frostbite

Cold Hands & Feet Overview

When your hands or feet (and sometimes other parts of the body, especially your ears and nose) get too cold, they can be injured or react in different ways.

  • The most severe cold injury is frostbite, which is true tissue freezing (ice crystals form in skin and other tissues of the body). Frostbite causes permanent damage to blood vessels and other structures. Frostnip is also ice crystal formation in tissues but only in the very outer layer of the skin. It causes no permanent damage.

  • Immersion injury results from exposure of wet feet (or hands) to cold temperatures at or above freezing. It develops over hours to days and damages the nerves and muscles. Like frostbite, immersion injury causes permanent damage.

  • Other injuries due to cold hands or feet are pernio, Raynaud syndrome, cryoglobulin formation, and cold urticaria.

Cold H...

Read the Cold Hands and Feet article »



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Frostbite »

Frostbite is a cold-related injury characterized by freezing of tissue.

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