The section on “cold stress” is interesting. For many years around high school and college I would get a 'cold" right after the first sharp drop in temperatures that led to the heat being turned on. We thought it was something to do with the heat stirring up more dust that was irritating my lungs/throat, but it seems that it more likely was what Cecil described - the body’s overreaction to the sudden drop in temperature.
Dried and cracked nasal mucous membranes caused by the cold, dry air can leave one more susceptible to the various allergens and microbial contaminants that might be more prevalent due to greater air flow through heating ducts.
My mother never told me wet feet would cause me to catch my death of cold, it was wet hair, and she was right. Every time I walked to the bus stop with wet hair when it was below - oh, say 35 F, I would get a head cold, and any one who says that’d not true does not understand the scientific method.
The various hypotheses that cold weather somehow has something to do with colds and flu, suggests a very obvious question we should ask:
When is cold and flu season Down South in the lands of the antipodes? In Oz, NZ, South Africa, do you get your cold and flu season in December-February? (If so, that might speak toward Cecil’s idea that going to church on Christmas is the culprit.) Or do you get your colds and flu in June through July when it’s cold and wet down there?
So, all our esteemed readers in the farther Southern latitudes, when is your cold and flu season?