You're perfectly healthy. You don't have a cold; you're not stopped up. But when you go outside in this freezing weather, your nose starts running. Ever wonder why?

It's pretty simple, says Dr. Steven Parnes, professor and head of the Division of Otolaryngology/Head and Neck Surgery at Albany Medical College in New York.

Your nose is a complex organ that helps you smell and taste but also warms, cleans and humidifies the air you breathe. In a normal person, the nose and sinus produce at least a quart of mucus every day.

This fluid helps keep the respiratory tract clean and moist. It doesn't make your nose run, because it eventually drains to the throat, and you swallow it.

But when you go outside in winter, your nose has to work extra hard to warm the cold air. Tiny blood vessels beneath the mucus-secreting glands dilate, or grow larger. That increases the blood supply to your nose, which increases the amount of mucus that your nose and sinus produce.

Because only so much can drain into your throat for you to swallow, the rest has to go somewhere. It drips out. And that is why your nose runs during winter.

What's not so clear, Parnes says, is why some noses in winter run more than others.

"Everybody's nose runs; your nose is lubricating itself," Parnes says. "But why do we have this overzealous reaction in certain people? That's one we can't answer. Some people just have more secretions than others."

TOM KEYSER,

Albany Times Union

Additional source: www.wisegeek.com.