Nasal membrane reaction to cold air
I finally know why my nose gets stuffy when it's cold out!
"When a person breathes cold air, the tissues lining the nose swell as the capillaries dilate, bringing warm blood to heat the cool air. Swollen capillaries in the nose are the cause of nasal congestion (nasal congestion is backed-up blood, not increased mucus). In addition to the congestion, the mucus in the nose, as we've said, increases and becomes thicker. This happens more in some people than in others. Thus cold air, by itself, can produce both nasal congestion and stuffiness. These can be treated with decongestants and/or antihistamines."
Interestingly, the symptoms temporarily subside while I am engaged in aerobic exercise, perhaps because adrenaline acts as an antihistamine. I've also read that nasal tissues are almost identical to penile erectile tissues, so I guess you could say that my nose is just really really excited all the time.
There's even a condition called "honeymoon nose," which is a sympathetic reaction of the nasal turbinates during a period of prolonged sexual stimulation. In other words, a stuffy nose is a sexy nose.
In my case, however, there's no doubt that the symptoms are brought on by nothing more than the cold air.