Editor's note: This popular story from the Daily Briefing's archives was republished on Jan 10, 2019.
There is a widespread belief that cold weather makes individuals more likely to catch a cold or influenza—and while that belief is mostly true, the reasons behind it might be surprising, Katie Heaney writes for The Atlantic.
According to a 2002 meta-analysis, exposure to cold does not in and of itself put you at risk of illness. Ray Casciari, a pulmonologist at St. Joseph Hospital in California, said, "If you took a person and you stuck them in a completely sterile room, and you raised and lowered the temperature, they wouldn't be any more likely to get infected."
Even so, many people believe that cold and flu become more common as the temperature falls.
What actually causes you to get sick in cold weather
According to The Atlantic, a change in humidity is likely the reason why people are more likely to develop a cold of the flu when the temperature falls.
According to Casciari, when individuals are in a low-humidity environment, their "eyes tend to dry out, the mucous membranes in [their] nose[s] dry out, and [their] lungs dry out, and [they're] therefore much more susceptible to bacteria and viruses."
Another factor is that during cold weather, individuals are more likely to cluster inside with friends and coworkers, creating an environment where bacteria and viruses can readily spread. "When you're (gathered indoors), where you're all really close together, and it's hot and humid because you've got a lot of people in there, that's when viruses like the common cold and influenza and certain bacteria actually spread," said Casciari.
Finally, according to Katharine Miao, the medical director at CityMD, some viruses find wintry temperatures welcoming. "Many viruses live longer and can replicate faster in colder temperatures," she said, adding, "As a result, a highly contagious virus such as influenza can stay active and linger for up to 24 hours on a hard surface."
To mitigate increased cold and flu risk, Casciari recommended using alcohol wipes to cleanse public surfaces, and Miao recommended using a humidifier to fight dry indoor air (Heaney, The Atlantic, 12/8).
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