Three days of being cold and wet appears to be a prudent timeframe within which to consider rotation of troops. In all studies from World War II, Korea, and recent experiences in Alaska, blacks had four to six times the incidence of cold injury of their white counterparts, matched for geographic origin, training, and education. Because long, thin fingers and toes cool more rapidly than short, fat ones, blacks' hands tend to cool faster than those of whites. However, more importantly, once cold, blacks stay cold longer because of a less potent CIVD response to their extremities. This does not say, however, that blacks themselves must be more vigilant in cold exposure and must take measures sooner to protect themselves from cold injury.
Place of origin has a significant role in cold injury susceptibility.
This response also improves in blacks from northern climates. This is not only a physiologic improvement in response to cold but a behavioral response as well. Knowing what clothes to wear, knowing when one's extremities are too cold, not being frightened of the cold, and knowing how to deal with cold extremities all add up to make cold-experienced individuals less likely to have cold injuries. Individuals with labile vasomotor conditions, such as Raynaud's, are also susceptible to cold injury. Cold injury tends to occur in passive, negative individuals.