Feb 21, 2013
The peak of flu season is behind us, but you may still be feeling its effects. In between your residual sniffles and lingering cough, you might be cursing the winter weather for making you sick. But does cold weather really cause colds (and flu)?
It’s no secret that flu season is worse during the coldest months of the year. For those of us in the Northern Hemisphere, flu epidemics strike from November through March; in the Southern Hemisphere, where seasons are reversed relative to the North, sickness peaks from May to September . Something about winter, it seems, is to blame.
But it’s not as simple as pointing the blame toward the thermostat. You need to be infected with a virus or a strain of bacteria to come down with the flu or a cold. It might be possible, however, that low temperatures make you more likely to get sick if you’ve already been exposed to a pathogen. Some scientists believe that being cold weakens your immune system, making you more susceptible to infection.
Researchers have been looking into this question for decades. Hundreds of self-sacrificing volunteers have spent hours in walk-in freezers, have walked around in wet clothing and have allowed researchers to drip infected mucus into their nostrils – all in the name of science. (Their dedication goes above and beyond what this writer would do in the name of science!)
But as it turns out, cold, wet and miserable volunteers are no more likely to get sick than their warm comrades. Being cold doesn’t make you sick – it just makes you shiver.
So why do so many people get sick during the winter?
One theory: It’s something in the air. Summer is hot and humid, whereas winter is cold and dry – and a growing body of scientists is trying to understand whether this affects flu transmission.
To test this theory, scientists at the University of California, Davis, infected a number of guinea pigs (real ones – not just the metaphorical kind). The scientists then exposed healthy guinea pigs to the sick guinea pigs under a range of temperatures and humidities. They found that the virus was most infectious in cold and dry conditions; something about the winter air made the healthy guinea pigs get sicker, faster.
Low humidity, the researchers suggest, allows the virus particles from a sneeze or cough to linger longer in mid-air; conversely, the high humidity of summer causes the droplets in a sneeze to condense and settle out of the air too fast for infection to occur . Studies show that warmer temperatures also kill pathogens quickly, sterilizing the sneeze.
The studies weren’t limited to guinea pigs; researchers studying at New York City’s weather data and public health records from 1975-2002 found that the death rate from pneumonia and influenza, while high all winter, spiked most prominently immediately after particularly cold, dry periods . So the cold, dry conditions of winter do seem to make it easier to get sick – not by weakening your immune system, but by making it easier for the virus to linger and spread.
Plus, let’s face it: when it’s cold outside, we all want to stay inside. People spend much more time indoors during the winter, putting us (and our germs) in close proximity to one another – perfect conditions for spreading sickness.
The conclusion? If you’re trying to avoid catching a cold this winter, a sneeze guard may be more important than a warm winter coat.