JACKI LYDEN, host:
Now, your runny nose may not seem like rocket science, but it does involve a bit of thermodynamics. What is it about the chilly winter breeze that makes tissues a cold weather essential? Earlier, I braved the great outdoors - and I know you can tell - to bring you this week's "Science Out of the Box."
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LYDEN: I'm standing on the roof of NPR headquarters in Washington, D.C. It's chilly. It's about 35 degrees or so. But earlier this week, especially on the National Mall, it was really cold. And I was suffering from what the experts call cold-induced rhinorrhea, and that colloquially is known as a runny nose.
We wanted to know why our noses always run in cold weather. So we called on Dr. Andrew Lane. He's the director of the Johns Hopkins Sinus Center, and he's standing outside his office in Baltimore. Welcome, Dr. Lane.
Dr. ANDREW LANE (Director, Sinus Center, Johns Hopkins University): Hi, Jacki. Thanks.
LYDEN: Well, I have been wondering this, really, since the first of the year. Why is it that our noses run in the cold whenever we step outside?
Dr. LANE: Well, it's really a combination of two things. It's part respiratory biology and part of it is physics, or thermodynamics. One of the main functions of the nose is to warm and humidify the air that we breathe so that when it reaches your lungs, it's nice and conditioned. And in order to do this, the nose has to add some moisture to it.
When it's very cold out, the air is usually dry as well, and the nose is really working overtime to add some fluid. And there are reflexes that are in place that allow the nose to increase its fluid production. And if it really makes a lot of fluid, then it starts to run out of the end of your nose.
LYDEN: So, it's a good reaction. It should happen.
Dr. LANE: Right. It's a normal reaction sort of taken to the extreme. Now the other side of it is the physics part. And this is sort of a good day for this, I suppose. Can you see your breath when you breathe there?
LYDEN: I can.
Dr. LANE: What's happening is that the warm air that you're breathing is condensing in the cold air, so you see it as little droplets of water. And that's because cold air can't hold as much moisture as warm air. When you breathe that air back out, it comes to the very tip of your nose where the nose is cold and that fluid is going to recondense onto the surface of the nose and that will also run out.
LYDEN: So kind of a double whammy on the old nose between the biology and the physics.
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Dr. LANE: Yeah.
LYDEN: Andrew Lane is the director of the Johns Hopkins Sinus Center. Thanks so much for joining us. I think we should both go inside and get warm now and have a cup of cocoa or echinacea.
Dr. LANE: I'm with you, Jacki. Thanks.