The reason for the common cold being so prevalent in cold weather is because of the cold.

My theory is that cold temperatures best suit the incubation of the germs. You are especially susceptible at night, when you can’t control your breath enough to keep your nose/nostrils warm. Warm face/nose at night = you won’t catch a cold.

I’m absolutely convinced of this theory. I’ve tested ways to keep my face/nose warm at night, and it seems to test very solidly (and I get sick very very easily). Once my room gets too chilly, I’ll inevitably wake up with a cold.