Ask Doctor K: Runny nose has variety of causes

DEAR DOCTOR K: Why does my nose run in cold weather? Does it mean I’m getting a cold?

DEAR READER: Cold air is not only cold, but also dry. The lungs are built to deal with air that is warm and moist. So, a main function of your nose is to make the air you breathe in warm and moist. Bones in the nose (called turbinates) are covered with blood-filled membranes. The blood running through the turbinates is at body temperature: around 98.7 degrees. The heat in the blood warms the cold air you breathe in.

The nose moistens cold, dry air by having its inner lining make watery mucus. It’s like a mini-steam bath with moisture dripping down the walls. The colder and drier the air, the more water and mucus need to be produced. This means more sniffles and drips.

Taking a warm shower or bath can help clear your sinuses and actually slow down your runny nose. You’re basically allowing the membranes to stop secreting mucus because the air you’re taking in now is already moist and warm. So a runny nose in winter doesn’t necessarily mean that you are sick.

Now to a question you didn’t ask: Why does your nose run when you have a cold? It runs for an entirely different reason. As the mucus leaves your nose, it takes the germs that are causing the cold out with it. It’s one of your body’s defenses against infection.

And another question: Why does your nose run when you have allergies? The reason is similar to why your nose runs when you have a cold. Your nose is trying to eliminate, to wash away, the substance causing the allergic reaction. That might be ragweed, dust, hair and dander from a cat, or many other allergens.

The watery mucus that comes out of your nose when you breathe cold air is clear. In contrast, mucus from a runny nose caused by an infection may become colored and opaque. That’s because the immune system cells that are fighting the infection get into the mucus. When you have such an infection, you can help your nose drain by taking hot baths or showers.