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San Francisco 49ers running back Frank Gore gets tackled by Green Bay Packers cornerback Micah Hyde during a frigid game on January 5, 2014, in Green Bay, Wisconsin. Cold temperatures have now returned to much of the country.



U.S. Cold Snap: What Do Bitter Temperatures Do to the Human Body?

Experts weigh in on how to safely weather the severe cold enveloping much of the country.

Thinking of taking a jog in the cold weather gripping much of the country? You may want to read this.

Subzero temperatures can do a number on your body in short order. According to experts, a wind chill of -50°F (-45°C) can cause frostbite in five minutes.

Experts say people—even professional athletes—should take cold snaps seriously.

During a past cold snap, we talked to Henderson McGinnis, a wilderness medicine expert and emergency physician at North Carolina's Wake Forest Baptist Medical Center, and Michael Lanigan, an attending physician in the Department of Emergency Medicine at SUNY Downstate Medical Center in New York City, about how the body responds to such frigid weather—and how best to handle it.

What happens to the body in extreme cold?

Our bodies are built to protect their most precious machinery—vital organs such as the heart, kidneys, and lungs. When faced with bone-chilling cold, we shunt all available blood to these organs to keep them warm and functioning. That means that "extremities take the hit for the rest of the body," said Lanigan, which is why your fingertips, toes, nose, and earlobes get so cold: They lose their blood. (Watch a video: "Human Body 101.")

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It's also why you may feel like urinating when you're in very cold weather: Your kidneys get a lot of blood flow. (Though "the last thing you think about doing [in the cold] is peeing outside," quipped McGinnis.)

Reduced blood flow to the extremities makes your legs and arms more sluggish. If you're out long enough and your body temperature starts to drop, your metabolism—how your body processes energy—also slows, causing mental confusion.

There's a saying that "cold makes you dumb," McGinnis said—meaning it's particularly dangerous if you have to make a crucial decision in the cold, like choosing a path on a hiking trail.

If skin is exposed for too long, frostbite—or skin damage caused by cold—can eventually set in. Whether someone gets frostbite depends on several variables, such as the person's health, the temperature, and the length of exposure.

How dangerous is it to be in extreme cold?

Prolonged exposure to severe cold is "a real risk," McGinnis said, though there's no real definition for "prolonged." Indeed, little is really known about how much cold is too much cold; doctors don't experiment on people because it would be inhumane.

Much of how you fare depends on your health and age: A healthy, well-prepared person in bitter cold for a few minutes will likely be OK. (See pictures of National Geographic explorers who have battled frigid extremes.)

Another factor to consider is the wind, which robs your body of heat more quickly than it can be produced. That's why biking or running in very low temperatures—which increases a person's pace and exposes them to more wind—is a bit more dangerous than walking, McGinnis said.

What's more, "it doesn't have to be a super-freezing or Mount Everest-type environment" to see the effects of cold if someone is outside long enough. As McGinnis noted, "We see people in North Carolina who have frostbite."

Lanigan added that his hospital in New York has already received some frostbite patients due to the cold snap.

What about professional athletes—especially football players who play in the brutal cold?

Playing football in temperatures below 20°F (-7°C) "is not smart," said McGinnis, "but it's not any more dangerous than getting hit by a linebacker."

But when you get into subzero temperatures, he said, it becomes foolhardy. The San Francisco 49ers beat the Green Bay Packers in Wisconsin on January 5, 2014, when the windchill was -10°F (-23°C)—one of the coldest games in NFL history.

Many players even wore short sleeves, which McGinnis called a "a macho thing" to psych the other team out. (Though "it didn't work in Green Bay," he quipped, "since [the Packers] lost.")

Most players were prepared for the cold, though, wearing gloves and using hand-warmers and covering their skin when they were off the field. Plus, said Lanigan, wearing short sleeves isn't quite as bad as wearing short pants, since the players' upper limbs are closer to their hearts and thus a bit warmer.

In general, athletes—even though they're in superb shape—may encounter additional effects from the cold because their constant motion forces blood to the extremities, taking the vital fluid away from the organs.

Exposing muscles to extreme cold also increases the likelihood of tears, sprains, and spasms.

What's your advice to people for weathering this cold snap?

First off, avoid being outside for prolonged periods. If you're going to be outside for a long time, cover up exposed skin—especially the face—and eat and drink water beforehand: Eating provides your body with fuel that can help you tolerate cold. Also, wear a windbreaker to prevent frigid gusts from stealing your body's heat.

If you start to feel pain or numbness, or notice your skin turning paler, go inside immediately: These may be early signs of frostbite. (And whatever you do, says McGinnis, don't rub the affected skin—that increases the damage.)

Perhaps the most important piece of advice? Always have someone else with you, says McGinnis, or at least tell someone where you're going. "Don't be Aron Ralston," the rock climber who kept his travel plans to himself, got stuck under a boulder in Utah, and had to cut off his arm with a pocketknife.

In other words, says McGinnis, "use common sense."

This story was originally published on January 7, 2014, and updated on January 4, 2018 with news of the cold gripping the country at that time.