system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do our noses run when it’s cold?
gpt
It's your body putting out fluids to keep the air you're breathing at a safe level of humidity and moisture for your lungs. If the air is too dry, your lungs can get damaged and prone to infection. When it's cold, the air gets drier, so your nose may start running to help keep the air moist.

Of course - colds are also more common in cold weather. Your nasal passages get dried out and damaged, which means viruses can get into your body more easily, causing colds. Additionally, you spend more time inside with the windows closed around other people who are more susceptible to colds.  So, you may find you just get more colds - causing runny noses - in the winter as well.