Every time I get a cold I wonder: Is it because I opted for slinky heels instead of boots when I went out last week? Or was it because I went outside with wet hair (something my mother always said would make me sick)? We’re all familiar with the plethora of warnings about bundling up to keep from catching a cold, but the truth is, colds and flus are viruses, so what does the cold have to do with it? Contracting some strand of rhinovirus is the real way you get the common cold, but that doesn’t mean the temperature has no bearing on whether you’ll get sick. Cold and flu season occurs during the colder months because of a number of factors. For one thing, in the colder months people are more likely to be crammed indoors, in close quarters where viruses can be passed around more easily. But that’s not the whole story. Studies have shown that the germs survive better in dry air. And in studies on guinea pigs, the flu virus passed the most in cold temperatures with low humidity. Viruses both survive and travel better in those conditions. And scientists have a few ideas as to why that is. For one thing, research released in 2008 found that influenza cells actually became stronger in the cold weather. The outer lining of the virus hardens in the cold, protecting it and allowing it to pass from person to person, where it can warm up, the coating melting so the virus is exposed and can infect the person. At the same time, many believe that the dry air causes nasal passages to dry, making them vulnerable to those viruses—though not everyone agrees on this theory. And other research has shown that the body has better defences against the cold virus when it’s warm. There’s still research to be done, but we know enough to put the old wive’s tale to bed: The cold does not cause colds or flu. As always, the best defence is a flu shot—unless of course you can escape the cold, dry weather and hide out in the tropics!