I’ve been wondering this for a couple of days, and it’s bugging the snot out of me! [sup]Ha! I slay me![/sup]
Anyone know?
Sorry, I don’t have an answer, but I do have a theory.
In the Grand Scheme of Things, I think some people are blessed with noses that don’t run. Those are the people that enjoy skiing, snowboarding, and long quiet walks in the woods in -48[sup]o[/sup] weather.
All other people were blessed with the Snot Factory nose. Those of us in the SF category hover at the windows in the winter wondering how in the hell those “other” people can stand the constant dripping, sniffing, dripping, sniffing, etc. It’s exhausting!
In this column, Cecil mentions “cold stress:”
http://www.straightdope.com/classics/a4_104.html
Cold stress is what makes your nose run when you’re not actually sick.
I’d speculate that a different mechanism is at play. To wit:
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The colder the air temperature, the less soluble water is in it (this is why warm moist air gives rise to rain as it rises and cools).
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In cold weather, you breath in cold air through your nose and the nasal passages cool off.
Therefore, in cold environments, moist air from your body gets cooled as it passes out through your nose. The water in it starts to condense. Your nose runs.
IMHO.
My theory is similar to Karl Gausses.
Cold winter air is much drier since it can’t hold as much water vapor. And your nose is trying really hard to stay wet so that its membranes don’t dry up and crack. And bleed sometimes like my hands often do in the winter.
Thanks guys!
I don’t think that’s it lesa (though, BLUSH I DID search, and missed that column…)… it isn’t a few-day thingy, my nose runs whenever I go out into the cold, and for a while after I get back into the warmth. And judging from the snuffling I hear around me, this is pretty common.
Karl and honkytonk: both of you have presented theories that make sense to me, but seem to be contradictory… both could be the reason…
Anyone able to bolster one, or offer another? 
I agree with Karl.
When Outside:
Your nose is cold and your breath contains a lot of moisture being exhaled from the lungs. It condenses on the cold surface of the inside of the nose, and starts raining.
When coming inside from the cold:
Notice how glasses fog up when you breathe on them, or come inside form the cold to the warmth? The same thing is happening to your nose but to a greater degree.
Experiment: Go into the cold for a specific period of time in order to cool your nose down to near ambient temperature. Next go inside and time how long your nose runs until it stops. Repeat the process as before, but when you come inside, try to warm up your nose as quickly as possible and see if the time is shorter for it to stop running.
I suspect that it’s worse when you come inside because the warm air is more humid so it condenses on the cold nose on both the inhale and exhale breaths. When you are out in the cold dry air, your nose will feel drier when you inhale deeply through your nose due to the low humidity.
Okay, but not only does my nose run, my eyes run too…I don’t suppose that condensing theory holds true for eyes too?
I was told by a biologist that a part of the reason for a runny nose in the cold is that the cilia and cells in the nasal passage which would ordinarily act to “trap” the sliding mucous are paralyzed in the cold, thereby allowing the mucous a free exit through the nostril.
Pairing that with the condensation theories, we may have a definitive answer.
I’ve just done a rather cursory MedLine search on this question.
It seems that a prominent component of the mechanism(s) responsible for a runny nose in cold weather is actually a reflex mediated through the cholinergic nervous system.
This was demonstrated by treating people (or one of their nostrils!) with an anticholinergic drug. In these experiments, pretreatment with atropine-like drugs relieved (but did not eliminate) the runny nose despite exposure to cold, moist air.
Thanks guys!
I knew I could count on you…
which begs the question: What on earth is the cholinergic nervous system?
Sorry, I missed your question.
The cholinergic nervous system is, in some sense, that part of your nervous system that slows the body’s functions down. It is the opposite of the sympathetic nervous system which governs the famous ‘flight or fight’ response.
But, in truth, it’s more complicated than that. The cholinergic system slows your heart, moistens your mouth, tears up your eyes, constricts your pupils, stimulates your bowels, relaxes your sphincters…
The chemical responsible for the effects of the cholinergic nervous system is called acetylcholine. Note the suffix, choline, whence cholinergic. The effects of acetylcholine are opposed by atropine.
Apologies for missing this last week.