How Cold Is Too Cold to Go Outside?

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The Midwest is freezing right now, and it's likely about to get even worse. Temperatures throughout the region are predicted to feel like minus 50 this week thanks to a polar vortex the National Weather Service has called "one of the coldest arctic air mass intrusions in recent memory." The Upper Midwest through the Ohio Valley will see a lot of record lows and potentially life-threatening wind chills, according to the NWS. So yeah, a huge portion of the country is facing some serious conditions—Chicagoans have declared it #Chiberia 2.0 and Minnesota has hit negative 53 degrees with the windchill. If you're not committing to holing up for the rest of the week just reading that, here's what you should know to stay safe. (Related: The Best Running Shoes for Winter Weather)

Being outside in extreme temps, even for minutes, can cause frostbite. Your skin, and sometimes underlying tissue, literally freeze, which in some cases leads to permanent damage, according to the American Academy of Dermatology. The AAD advises bundling up and staying hydrated, and if you start experiencing frostbite symptoms—redness, stinging, or throbbing followed by numbness—head indoors. And if your skin turns gray, go straight to the ER.

Even more serious is hypothermia, a dangerously low body temperature. It can affect a person's brain so they're unable to think clearly and grasp what's happening, according to the CDC. If someone is shivering, confused, and/or has slurred speech, the CDC advises taking their temperature. If it's below 95 degrees, seek emergency medical help pronto.

Of course, your risk of frostbite and hypothermia is higher in colder conditions, so it's helpful to know where the line is between frigid and downright dangerous if you have plans to head out. A good rule of thumb is to stay in when the temperature drops below 0, or if the windchill is below minus 17 degrees, according to Robert Segal, M.D., cofounder of Labfinder.com. If you'll be exercising, you might experience an asthma-like condition called exercise-induced bronchoconstriction. "During exercise when we inhale cold air, the tubes in the lungs that carry air constrict," explains Dr. Segal. This can lead to coughing, wheezing, chest pain, and shortness of breath, he says. Also, just because you'll be working out doesn't mean you'll be protected against hypothermia. "Because the body is producing heat while exercising, it is better to run than just walk, but it's still not recommended in severe weather conditions," says Ehsan Ali, M.D., of Beverly Hills Concierge Doctor. (If you're planning to run during the winter, read our guide to cold-weather running.)

When you do opt to venture out, take safety measures to protect yourself from cold air. Wear layers and make sure every part of your body is covered to trap body heat, Dr. Ali advises. (Here's how many layers you should wear during a winter run.) And when in doubt, wrap up in a blanket burrito-style and stay home.