SUNDAY, Feb. 20 (HealthDay News) -- Having "Jack Frost nipping at your nose" sounds swell when Nat King Cole sings it, but frostnip and frostbite can be serious cold weather hazards, experts say.

Cold weather causes the blood vessels to narrow and constrict, reducing blood flow to the ears, nose, and the upper and lower extremities, including the hands and feet, while shifting blood flow to the vital organs.

"The body shifts warm blood from its extremities to its center where the organs most vital to survival are," said Dr. Melanie Cerinich, an emergency physician at Loyola University Medical Center in Maywood, Ill. "Since the extremities receive less warm blood, they become more vulnerable to cold."

Frostnip -- which sets in before frostbite and is less serious -- commonly affects the fingers, face, ears, toes and other parts of the body overexposed to cold.

With frostnip, the skin of the affected area is stiff, numb and white but the tissue underneath is still warm and soft.

"Treatment for frostnip is as easy as warming the affected area by rubbing, moving and covering it up with extra layers of clothing. You can also dip the frost-nipped area in warm -- never hot -- water until normal sensation returns," Cerinich said in a Loyola news release.

Frostbite occurs when a part of the body actually freezes. With mild frostbite, the affected area may be numb and the skin may appear white, gray or blistered.

Treatment for mild frostbite is similar to treatment for frostnip, Cerinich said.

In severe frostbite, the tissue underneath the skin can be frozen to the bone. The skin will be hard, numb and appear pale, white or gray. Severe frostbite can lead to gangrene, amputation and even death.

"People with severe frostbite should never rub or apply snow to the affected area. This will only increase injury to the tissue," Cerinich said. "The best thing to do is to get out of the cold as fast as possible and wrap the frostbitten area immediately in some warm clothing or warm it with your body. Then seek immediate medical attention."

To reduce the risk of frostnip or frostbite, limit your exposure to extreme cold; wear dry, layered clothing; don't forget a hat; and use mittens, which are warmer than gloves.

More information

The U.S. Centers for Disease Control and Prevention has more about cold weather health dangers.