updated 1/7/2010 3:38:40 PM ET 2010-01-07T20:38:40

Extremely cold weather has descended upon most of the nation this week, and this frigid air may have you feeling like you could "freeze to death." Paranoia aside, when temperatures dip, frostbite and other health risks are real concerns. And death strikes long before the body actually freezes.

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Yet our bodies are pretty hardy, as we have two built-in mechanisms to protect us from the cold.

As soon as that bitter air hits your face, your body will try to insulate itself by moving blood away from the skin and outer extremities, such as fingers and toes, and toward its core. This process is called vasoconstriction, and it helps limit the amount of heat you lose to the environment, explained John Castellani of the U.S. Army Research Institute of Environmental Medicine (USARIEM).

The second response from your body is shivering. People may experience a little shivering when they're skin temperatures starts to fall, but major shivering usually doesn't occur unless your core body temperatures drops, Castellani said.

Death without freezing
An unusually low body temperature is called hypothermia, and the average person will usually not experience this during a stint in the cold, Castellani said. But if you're wet and cold, it’s a different story, since your body loses heat about 25 times faster in water than in air, according to Michael Sawka, chief of the Thermal & Mountain Medicine Division at USARIEM.

People can even develop hypothermia at temperatures above freezing if it's raining.

Normal core body temperature is 98.6 degrees Fahrenheit, and mild hypothermia sets in at about 95 degrees Fahrenheit. After that, "as you start dropping [in temperature], bad things happen," Sawka said.

  • At 91 degrees Fahrenheit, you can experience amnesia.
  • At 82 degrees, you can lose consciousness
  • Below 70 degrees Fahrenheit, you are said to have profound hypothermia and death can occur, Sawka said.

The record for the lowest body temperature at which an adult has been known to survive is 56.7 degrees Fahrenheit, which occurred after the person was submerged in cold, icy water for quite some time, according to Castellani.

Frostbite danger
On the other hand, frostbite, an injury caused by freezing, is more common in everyday scenarios.

"It takes a lot to drop the core body temperature down, but it doesn’t take as much to drive the peripheral temperatures down," Castellani said.

Your fingers and toes are more prone to frostbite, because those areas will have reduced blood flow in cold temperatures, as your body tries to keep its core warm. Even though your feet are usually protected by shoes, toe temperatures can get very low, and if you sweat, the wetness will draw even more heat out of the area.

Since frostbite is brought on by freezing, you can't get frostbite if the air temperature is above 32 degrees Fahrenheit. And frostbite is more common at pretty low temperatures, well below freezing. "It takes a wind chill temperature of around minus 15 degrees [F] where you start to see an increase in the incident of frostbite," Castellani said.

How long it takes you to develop frostbite will depend on the conditions. For example, if it's 0 degrees Fahrenheit with a wind chill of -19 degrees Fahrenheit, you could be frostbitten in 30 minutes, but if it's -15 degrees Fahrenheit with a wind chill of -55 degrees, you could get frostbite in as little as 5 minutes, according to the National Weather Service.

Despite these risks, "Human beings can go out in very extreme cold environments and do very well," Castellani said. People climb mountains, trek in the Arctic, and swim the English Channel, which has very low water temperatures.

And people who expose themselves to cold frequently can adapt to the frigid temperatures, producing and retaining heat more effectively, Sawka said.

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