It is the inability to physiologically compensate for cold that produces injury. However, cold itself is not the only factor in determining whether injury will occur. Duration of contact, humidity, wind, altitude, clothing, medical conditions, behavior, and individual variability all contribute to the picture.

Cold-induced injury may be instantaneous, as with contact frostbite after touching a cold metal bottle of fuel, or more chronic, as in chilblains. Humidity is also important because it contributes to evaporative heat loss. Wet skin is more conducive to both subcutaneous ice crystal formation and trench foot. Wind velocity and cold, the wind-chill factor, have a synergistic effect on heat loss. For example, an ambient temperature of -7°C (19.4°F), when combined with a wind of 72.5 kph (45 mph), will feel equivalent to -40°C (-40°F) on a windless day. The rigors of travel at high altitude may also predispose to cold injury. Although the lower barometric pressure has not been shown to directly influence susceptibility to cold injury, a variety of factors associated with high altitude travel have. The fatigue, dehydration, and hypoxia often seen in climbers or trekkers, coupled with the sometimes extreme weather conditions and remote locations, all contribute to the incidence and severity of cold-related injuries at high altitude. 1

Inadequate clothing is probably the most avoidable cause of cold-related injuries. Constrictive clothing and boots can reduce circulation to extremities and predispose to frostbite. An exposed head and neck can account for 80 percent of body heat loss. Natural-fiber clothing, such as wool and cotton, when compared to modern synthetics, such as polypropylene, have poorer wicking ability and greater thermal conductance and moisture retention. 1 Simply changing out of cold, wet clothes into dry ones can also be preventive. During World War I, the British decreased the number of trench foot cases from 29,172 in 1915 to a total of only 443 in 1916-1918 by frequent foot drying and sock changing.23

Certain disease states, such as atherosclerosis, arteritis, hypovolemia, diabetes, vascular injury secondary to trauma or infection, and previous cold-related injuries, may predispose to cold-related injury.

Individual behavior is extremely important as well. In fact, alcohol- or drug-intoxicated persons, combined with psychiatric patients, account for the majority of frostbite cases in the United States. Impaired judgment and lack of self-preservation instincts prevent these populations from dressing adequately and making rational decisions about exposure to the cold. Alcohol consumption also increases peripheral vasodilatation and heat loss, which increases the risk for hypothermia. In addition, many of these patients smoke, which results in peripheral vasoconstriction and increases the risk of frostbite. 1 Other examples of the precipitation of cold injury by individual behavior can be seen in recent case reports of significant facial frostbite by inhalation abuse of fluorinated hydrocarbons (e.g., Freon) and nitrous oxide.45 There have also been case reports of full-thickness frostbite resulting from inappropiate use of dry ice as a first-aid cold pack. 6

Military studies suggest that dark-skinned soldiers and those from warmer climatic regions are more susceptible to frostbite. Conversely, peoples indigenous to frigid climates, such as Eskimos, Tibetans, and Laplanders, are often "acclimated" to the cold and are less prone to injury.1

Local cold-related injuries are classified into nonfreezing and freezing injuries.

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