So, you’re on a first date, skating at your local outdoor ice rink on a frosty winter
evening.
Your partner grabs you by the hand, looks at you longingly in the eyes, and sees one
wet, runny booger coming out of your nose.
You sniffle and snuffle but your nose just won’t stop running.
When it comes to your runny-nose embarrassments, you can blame both biology -- which makes
your body produce more mucus -- and physics, which turns some of the water vapor you inhale
into liquid.
On the biology side, your nose starts producing more mucus to warm and moisturize all that
cold, dry air. Some of the mucus drains out your nose for the whole world to see -- in
what doctors call rhinorrhoea [rhino-ree-uh].
The mucus dripping from your nose comes from your mucous membrane -- the thin, protective
blanket of cells that covers the inside of your nasal cavity.
The mucus is mostly made of water, salts, and white blood cells and glycoproteins -- or
proteins that are attached to carbohydrates.
When air gets colder and dryer -- like in the winter -- your mucous membrane is triggered
to secrete more mucus, which moisturizes the air so your nasal cavity doesn’t dry up,
crack and bleed.
As a bonus, the mucus traps particles in the air, stopping a lot of the harmful stuff from
getting into your lungs.
Now after you inhale you end up with two nice warm lungfuls of air, ready to be exhaled
-- which is where the physics comes in.
Some of what you exhale is water vapor, and when you exhale, it’s suddenly pushed from
a nice, warm environment to a harsh, cold environment.
The sharp change in temperature causes that water vapor to condensate into little water
droplets on the tip of your nose -- the same way water condensates on the cold bathroom
mirror while you’re taking a hot shower.
All of a sudden, you’ve got water dripping from your nose, you’ve got mucus dripping
from your nose, and this date is not going very well. Next time, just go bowling.
Thanks to patreon patron Heather Thornburn for asking this question, and thanks to all
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