Runny nose in cold wind: are you catching a cold?

The inside of the nose is lined with a thin mucous membrane with plenty of blood flowing beneath it. In the brief moment that inhaled air brushes past it, the air is warmed to near body temperature and becomes almost fully saturated with moisture. Freezing, dry air doesn't hit your lungs directly because the nose takes on this job.

When the air is cold and dry, the membrane has to give up much more water. Nerves in the nose then signal the glands in the lining to release more fluid. In experiments, spraying a drug that blocks those nerve signals into the nose beforehand greatly reduced cold-induced runny nose, which confirmed that it's a nerve-driven reflex.

Some of the drip also comes from the breath you exhale. Exhaled air is warm and full of water vapor, and as it passes the chilled tip of your nose it cools and condenses into tiny droplets. The tip of the nose sticks out furthest from the face, so it's also the first place the wind cools down. It's the same thing that makes glasses or windows fog up on a cold day.

That's why a cold-weather runny nose tends to be clear and watery. Once you're back in a warm room, it usually eases within a few minutes. How much comes from the nasal reflex and how much from condensing breath varies with the person and the weather, so it's hard to split neatly.

It's easy to think cold wind gives you a cold and that's why your nose runs, but colds are caused by viruses passed from person to person. A cold-air runny nose happens without any virus, and it showed up about equally in people with and without allergies. In one survey of 90 patients at a ski resort clinic, 96% said cold exposure gave them a runny nose.

In daily life, lightly covering your nose with a scarf or mask warms the incoming air a little, and your nose tends to run less. A few tissues are enough. If the mucus turns thick and yellow, or comes with a fever and sore throat, it's hard to put it down to cold air alone.