Wind chill measurements are more important than air temperatures when it comes to evaluating the dangers of cold weather, Castellani said, because the wind chill describes the temperature your skin is actually experiencing.
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Fingers, toes, noses, earlobes and cheeks are most vulnerable to frostbite, he added, because peripheral areas are the first to experience vasoconstriction and blood loss after exposure to cold.
After being chilled for a while, many people experience something called cold-induced vasodilation (CIVD), which dilates the blood vessels in the extremities, causing a sudden hot, burning sensation.
People with good CIVD responses deal better with cold than those who easily lose circulation to their fingers and toes. People with a condition called Reynaud's phenomenon, which disproportionately affects women, do not experience CIVD at all and are particularly vulnerable to frostbite.
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Another concern on super-cold days is that frostbite can happen almost instantly if, say, you touch a frozen metal door handle or come into contact with gasoline, which can get down to -40 degrees Fahrenheit or colder and remain a liquid. Rolling down your car window to adjust the side window while driving fast on a cold day is also a bad idea.