POP QUIZ:

Everyone knows that we get more colds when the weather turns colder, but why is that?

* Answer on S4

ANSWER: We spend more time indoors with the windows closed, which allows infections to spread more easily; there is less sunlight, and ultraviolet light is known to kill viruses; the stress and increased activities of the holidays can weaken the immune system; cooler air may cool the nose and allow cold viruses to replicate at a higher rate. (Question on S1.)