[jamest (OP)]

Charlene writes in to ask:

'Why is my nose constantly running in cold weather? What is the physiological benefit of this?'

[Zer0]

Donno why it's Runny.
Maybe an Immune response from the body.

I read Mucus prevents bad biological stuff from getting inside of the Nose by flushing it out.

ps - Be Patient, detailed & precise Responses shall arrive soon.

[paul cotter]

I suspect there is no advantage and it is just a normal physiological reaction just like cold air creates goosebumps(piloerection to be scientifically correct). When the air temp drops there is less evaporation occurring in the nasal mucosa and the excess drips out. I was once doing a commissioning in a freezing cold mv switch room when my test equipment started to malfunction with the backlight of the display failing. This required me to lean over the gear to read the display and then my nose started streaming and worse, I had no tissues! I was surrounded by a coterie of suited consultants and it was so embarrassing, every time I leaned over I had to use my hand to wipe away streams of mucus.

[alancalverd]

Normal physiological reactions have all evolved over time as the most parsimonious protective response to a challenge. Piloerection makes sense if you have proper mammalian fur - it increases the thickness of trapped air, thus reducing convective and conductive heat loss,  and is more comfortable than a string vest.
So I support Zero's assertion that nasal mucus is a means of trapping and flushing an irritant. This makes obvious sense when the irritant is dust  but needs a bit more speculation when it is a viral infection. My guess is that the primary response is inflammation  caused by the immune system doing its job, and this is detected by the nervous system as being the same as mechanical irritation so  you get the same mucus release.

[paul cotter]

Alan, I agree with what you are saying but I was under the impression that the op was querying the effect of cold temperatures rather than the viral cold.

[vhfpmr]

If I keep licking my lips in cold dry weather and leave it to evaporate, my lips become cracked and sore. If the lining of the nose is the same, I can see some benefit in preventing it from drying out.

[alancalverd]

Indeed. Cold air generally has a lower water content than warm, and the warm inner surface of the nose will cause more water to evaporate so it needs to be replenished or protected.

[Zer0]

On second thought...

Seems apt if the Body is simply reacting to the Difference between Temperatures.
(Hot/Cold)

But Immunoresponse towards a Virus or Infection by Flushing it out of the nasal passage and taking into consideration the Mouth is right underneath seems a bit off.

Hmm...does the Mucus disinfect or Neutralize  the infection/virus?

Or is it that Certain Things can be Fatal going up the Nose n entering the Lungs.
Vs
The same Thing going inside the Mouth n landing in the Stomach.

ps - now that's an interesting question.
Thanks@Charlene!