A Quart of Mucus Every Day
First, here is a gross, but interesting body fact for every preteen - our bodies make about a quart of mucus each day.
The purpose of the mucus is to keep the respiratory tract clean and moist. It does not usually make your nose run, it just drains into your throat and you swallow it.
However, when you go outside into the cold weather, your nose tries to warm the cold air, dilating tiny blood vessels under the mucus-secreting glands, increasing the blood supply to your nose, which increases the amount of mucus produced - how cool is that?
Since only so much mucus can drain into your throat to be swallowed, the rest comes out your nose - which is why your nose drips on cold days. OK, call me silly, but I think this is a really interesting factoid! Thanks for letting me share it with you.
Photo credit: jeffK