Exposure to bitter cold air may trigger breathing difficulties in those with asthma or broncho constriction, which in some instances may be life-threatening, says an asthma expert at the University of Medicine and Dentistry of New Jersey (UMDNJ).

Broncho constriction, which is characterized by prolonged coughing, wheezing, chest tightness when exhaling and shortness of breath, and hypothermia, a dangerous chilling of the system, send people to hospital emergency rooms each winter, says Dr. Leonard Bielory, director of the Asthma and Allergy Research Center at the UMDNJ-New Jersey Medical School in Newark.

"People who experience any form of broncho constriction, particularly children, should avoid exerting themselves in extreme cold," Dr. Bielory said. "When going outside, they should keep their heads and faces with a hat and scarf."

Jogging, especially in bitter cold weather, is a tremendous strain on the lungs, Dr. Bielory said. "Exercising at a health club is preferable to outdoors during the winter season, especially when temperatures plummet."

Why do respiratory conditions and colds occur more frequently in the winter than in other seasons? "The theory is that most of us spend considerably more time indoors where viruses can be passed between those in close contact," Dr. Bielory said.