Exposure to sub-freezing temperatures for as little as two or three minutes can cause frostbite, Margaret A. Mahoney, a registered nurse at Massachusetts General Hospital (MGH), said yesterday.

Temperatures reached minus three degrees yesterday and are expected to dip to around zero today, according to National Weather Service reports.

Frostbite is a "reaction to severe cold when the blood vessels in one part of the body construct and then close off, if the frostbite is not treated," Mahoney, who works in the MGH screening clinic, said.

If the frostbite is not checked, the tissues affected can die, and an infection, usually gangrene, follows the death of the tissue, she added.

"As far as I know, there have been no cases (of frostbite) reported at UHS (University Healty Services) today or yesterday," Warren E.C. Wacker, director of UHS, said yesterday.

"'Keep warm, keep moving and keep dry' sort of sums it up in seven words," Mahoney said.

Saving Face

"Needless to say, anything that promotes warmth is good," she added.

Mahoney said people should avoid exposure to cold for "extended periods in cramped positions or with constricting clothing because they can help to stop circulation."

People with diabetes or other circulatory or vascular diseases are especially susceptible to frostbite and should take special care to avoid prolonged exposure to the cold, she said.

Abusers of alcohol and tobacco are also more highly susceptible, she added.

If a person contracts frostbite, he should immerse the affected part of the body for 20-30 minutes in a large container of water heated to between 104 and 108 degrees Fahrenheit, Mahoney said.

A frostbite victim "should not use dry heat like a stove or a heating pad and should keep the extremity free-floating in the water and not rub it," she added.