Extreme Freeze: How Cold Can a Person Get?

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Temperatures plummeted so low in parts of the nation this week that many schools and businesses closed, concerned that people would get stuck outside for too long in such frigid weather.

In Minneapolis, where I live, Monday dawned with a wind chill of 45 degrees below zero Fahrenheit. One of our cars started but the other was stuck for two days because the garage door froze shut.

Inconveniences aside, how dangerous is the cold, really?

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The answer is slightly different for everyone, experts say, depending on body size, body shape and layers of warm clothes worn. But overall, people don’t have a lot of biological tools for adapting to cold conditions. When wind chills fall into the double digits below zero things can go bad quickly.

“In general, humans are not very well adapted to be able to do well in the cold, short of having a very large brain,” said Christopher Minson, an environmental physiologist at the University of Oregon, Eugene. “There are some physiological responses that help, but the main thing we do is put more and more clothes on.”

When you step outside on a cold day, your body initially reacts by constricting blood vessels in the skin and diverting blood from the periphery to your core in an attempt to limit heat loss by lowering the temperature gradient between skin and environment.

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As your core temperature drops below the normal average of 98.6 degrees Fahrenheit, you start to shiver, which generates a little heat, Minson said, but not a lot.

At a core temperature of 95 degrees Fahrenheit, you’ll feel uncomfortably cold. That’s when mild hypothermia settles in and the body begins to have trouble maintaining its internal temperature.

When it drops to 91 degrees Fahrenheit, Minson said, people develop amnesia. They become irrational and do strange things like taking all of their clothes off, thinking that they’re burning up instead of freezing cold.

At internal temperatures of 82 to 85 degrees Fahrenheit, people lose consciousness. Death comes at a core temperature of 74 degrees Fahrenheit.

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One reason hypothermia is so dangerous is that the body’s enzymes and nerve signals work best in a warm system. When the system gets colder than it should be, processes slow down.

Frostbite is an even bigger concern during cold snaps like the one we’re experiencing now, said John Castellani, of the U.S. Army Research Institute of Environmental Medicine in Natick, Mass.

When wind chill is below -17 degrees Fahrenheit, there becomes a very real risk that uncovered skin tissue can freeze. Ice crystals that form in skin cells can cause damage, including cell death. The early stages of frostbite is called frostnip, which is freezing at the surface of the skin.