[FuzzyUK (OP)]

Why do noses drip in cold weather, even though one does not have a cold?

[Chemistry4me]

It has to do with the mucous membranes in our nose, the mucous membranes heat the air we breathe in like a heating system to about 30 degrees in fractions of a second. We pump one half to a liter of air into our lungs with every breath we take, increasing to up to ten times as much on exertion. When it’s cold outside, the mucous membranes can only do their job by producing greater amounts of watery mucous at the same time – and that’s when our noses run.