This extreme cold in Chicago can be dangerous to people who must venture outside.
Doctors say it's important to cover up completely and not let any skin be exposed for more than a few minutes.
They warn to watch the skin for the signs of hypothermia and frostbite; those signs include redness, numbness, discoloration and pain.
Mental confusion is also an early sign of hypothermia.
Doctors recommend, if you are exposed to the cold for long periods of time, you should warm up gradually and avoid pouring hot water on your hands.