Why does cold weather help cold and flu viruses?

THAT'S THE WHY:"Wrap up or you'll catch your death." Why is it that we tend to link cold weather, or even just being cold, with catching the common cold or the flu, complete with a stuffed-up nose, headache and attendant misery?

Merely being cold won’t give you a common cold or the flu – for that to happen you need to be infected with a cold or flu virus.

But there are some suggested reasons why cold weather could mean you are more likely to be exposed to such viruses.

Cold and flu viruses infect the upper respiratory tract, and they can be spread from person to person through direct contact or via airborne droplets sent out when an infected person sneezes.

In colder seasons, people tend to gather indoors rather than in the open air, which could offer the viruses greater opportunities to spread between hosts.

Cold and dry air also seems to make it easier for the flu virus to spread through the air, if observations from a study that housed infected and non-infected guinea pigs together under various conditions is anything to go by.

“Twenty experiments performed at relative humidities from 20 per cent to 80 per cent and 5°C, 20°C, or 30°C indicated that both cold and dry conditions favour transmission,” wrote the authors in PLoS Pathogens in 2007.

“Our data implicate low relative humidities produced by indoor heating and cold temperatures as features of winter that favour influenza virus spread,” they noted.