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Q. Do air-conditioners cause sinus congestion?

A. Yes, air-conditioners can make some people’s noses clog or run, for several reasons.

First, walking into a cold, dry room can trigger a runny nose, just as walking outside on a cold winter day drives many people to reach for tissues, said Dr. John Ohman, chief of the division of allergy at Tufts Medical Center in Boston. The cold air seems to trigger nervous system reflexes in the nose that cause glands in the nasal membranes to produce mucus; the problem may be particularly common in those with allergies. But changes in temperature and humidity should trigger only brief congestion, Dr. Ohman said.

Those with allergies might develop congestion because small particles like pollen, mold spores, pollutants and dust mites can get trapped by air-conditioning filters and then released into the air when the machine is turned on, said Dr. Maria Garcia-Lloret, an allergist at the U.C.L.A. School of Medicine. Pollutants and bacteria wouldn’t cause an allergic reaction per se, she said, but could irritate the nose. Exposure to mold spores can cause allergic reactions that may be particularly long-lasting.

Dr. Richard Lebowitz, a rhinologist at NYU Langone Medical Center, emphasized the importance of changing air-conditioning filters regularly. “If you don’t maintain them well and everything you breathe is filtering through this gigantic sheet of dust,” dispelling dust into the air, “that’s not very helpful,” he noted.

Air-conditioners with clean filters can actually reduce sinus problems by keeping allergens out of the air, Dr. Lebowitz said. But there’s no way to avoid the runny nose that comes from changes in temperature and humidity. “Live with it — or sweat,” he said.