Is this an 'old wives tale'?
"You should not go out if you have a cold."
One concern is infecting others.
Aside from that I wonder if there is any scientific health basis for the idea that one should stay inside.
Another one is my mother used to always say, 'don't go outside with wet hair, you'll catch a cold'- I wonder about that too-
I can't see any reason why having a wet head would make one more likely to catch a cold.