People spend more time inside in enclosed spaces with others, dry air thins your mucus linings and also allows particles to stay in the air longer, less sunlight equals lower vitamin d levels, and on top of it all, certain viruses love cold dry weather.
A doctor said one of the reasons cold and flu “season” tends to be October through January isn’t because of germs being extra crazy, but because of all the holidays and the increased eating of bad foods which in turn make us more susceptible to germs.
Makes sense.