It can progress quickly especially in weather like what's coming, so the key is knowing the signs to catch it early.
On Friday, as kids hit the sledding trails, many didn't stay outside long. The cold air felt biting.
"It burns but not in a hot way, in a cold way," said Simon Curry of Havertown, Pa., as he chuckled.
He's describing frostnip - the first stage of frostbite.
Your skin may turn red, feel cold, and that sensation can turn into prickling and numbness.
The areas most at risk are the fingers, toes, ears and nose.
In the second stage of frostbite, red skin turns white or very pale. It may feel deceptively warm, and blisters may show up after the skin is warmed.
Severe frostbite goes through all the layers of the skin. You'll lose your sense of feeling, and the tissue will die, causing permanent damage.
Both the second and severe stage of frostbite need medical attention.
To avoid problems, as the extreme cold rushes back in, bundle up!
Parents when dressing kids, add one more layer than you would wear to keep warm.
And cover those high risk areas.
"Two pairs of gloves, two pairs of socks so I am doing my best to stay warm," said Bridget Johnson of Drexel Hill.
It also helps to move around BEFORE going outside. Don't break a sweat, but do get your heart pumping. And then don't stay outside very long.
If however, you have those early stages of frostbite, you want to warm the area SLOWLY.
* You can put your hands or feet in warm water (not hot).
*Cover other areas with a blanket
*Don't use a space heater or fireplace
*Don't rub the area