It is not cold feet and wet heads that are the problem, infectious disease experts say, but the fact that human beings are warmth-loving social animals.
At least in cold climates, widespread outbreaks of diseases like colds and influenza tend to start in winter months, when people spend more time together indoors in close quarters with the windows shut.
The cold months also bring children, those well-known vectors of bacteria and viruses, together in the classroom and day-care center, where they can pick up infections and take them home to the rest of the family.
In the Northern Hemisphere, early winter also includes major holidays with their attendant crowds and socializing. And even air-kissing under the mistletoe and New Year’s handshakes may help transfer germs, some of which travel in airborne respiratory particles while some are spread from hand to hand.