This from the Iowa Department of Public Health -- and it is useful as I just walked in the paper from outside:
The Iowa Dept. of Public Health (IDPH) has received several inquiries regarding the length of time it takes for skin to freeze in the predicted wind chill ranges for tonight and tomorrow. According to the National Weather Service, wind chills will range statewide from 30 to 40 below zero overnight and tomorrow morning when people will be going to work and children will be going to school. In those conditions, exposed skin could freeze within 10 minutes.
It is best to stay inside if possible, but if you must be outdoors during these extreme conditions, it is very important to protect yourself against frostbite. Cover all skin, including hands, head and ears, neck and face, if going outdoors for any length of time, even if only for a few minutes.
Frostbite causes a loss of feeling and a grayish color in affected areas. It most often affects the nose, ears, cheeks, chin, fingers, or toes. Frostbite can permanently damage the skin, causing scarring, and severe cases can lead to amputation. Signs of frostbite include a white or grayish-yellow skin area, skin that feels unusually firm or waxy, or numbness. A person is often unaware of frostbite until someone else points it out because the frozen tissues are numb.
If you must be outside for any lenghth of time, make sure you check yourself and your children for these signs. If your skin shows these signs of freezing, go into a warm place immediately. Warm up frozen/chilled skin by pressing agaist normal temperature skin (put frozen fingers in airpits). Do not massage frozen/chilled skin, do not rub with snow, or place hot items against skin as this could cause more damage. Seek medical attention if skin does not quickly return to normal color or pain occurs and continues.