When it's this cold, it can get very dangerous outside very quickly.

The most dangerous thing when it's this cold is unprotected exposure, according to Dr. Donald Carr, an internist at Wheaton Franciscan Health Care.

"In other words, unexposed skin, the wind, dropping temperatures, and moisture."

Dr. Carr says frostbite can develop on exposed skin within minutes.

"You just feel a little numb and cold on the skin, and you don't think much of it, and it may hurt initially and the pain may settle, and you think it's not bad, but if you're not paying attention and covering the skin, it only gets worse, and then it becomes more numb, and hard, and then it can become a problem."

That can include severe tissue damage or the onset of hypothermia.

"When the core temperature starts to drop, you're losing heat from your entire body much faster than you can produce it, and as the temperature gets lower and lower, your ability to move, think, to help yourself starts to diminish," warns Dr. Carr.

"If you are not able to get out of the cold, unfortunately, that only gets worse."

Dr. Carr recommends that people who have to be outside ought to have more layers than what they think they may need for the forecasted conditions.

"Be prepared, perhaps, for temperatures that are even worse than what they're predicting," suggests Dr. Carr. "If you're stuck longer, if you're stranded, if you're waiting for the bus longer, you'll be able to help yourself.

"Keep the wet out, keep the wind out with your clothing, and keep the warmth in. That usually requires layering. The outer layer should be wind resistant. It doesn't let the wind through.

"You should use (the inner layer) to keep the moisture off your skin. Wool, and synthetics are best. Cotton tends to hold the moisture of your skin right against your skin."