It’s a universal piece of home-baked health advice, passed down through generations: Bundle up before you go outside — you’ll catch a cold! But do chilly outside temperatures actually cause the common cold? The answer is more complicated than you might imagine, but at a time when we’re all acutely aware of the potential spread of viruses — COVID-19 foremost among them — let’s look into what’s real or not about our conceptions of the common cold.
Incubating the Common Cold
The common cold is not caused by the weather nor by frigid temperatures, but by viruses. More than 200 different types of viruses can cause a cold. The most prevalent, however, is called rhinovirus, which is responsible for nearly half of America’s sniffles. Most people pick up rhinovirus because they come into direct contact with a sick person, they inhaled the virus through infected droplets suspended in the air, or they touched a contaminated surface. Most of this contact occurs in crowded places or indoors. In fact, one of the last places you’re likely to catch a cold-causing virus is outside while you’re enjoying brisk, fresh air.
But that’s not to say chilly temperatures aren’t a contributing factor. They are.
When cooler weather strikes, the prevalence of outdoor activities like al fresco dining or socially distant meet-ups at the dog-run shrinks. And as cold weather drives us indoors — especially into close quarters — our chances of coming into contact with a contaminated person or object increases. Furthermore, cold weather often compels us to crank up the thermostat, which can lower indoor humidity. In a hot, dry room, your body’s nasal mucus — the frontline defense for stopping a cold early — is greatly reduced, weakening your immune response. To make matters worse, some viruses are more likely to hang suspended in the air when the indoor environment is extremely dry.
But warm, dry indoor air isn’t the only culprit. The cold shares blame, too. Rhinovirus thrives in cooler temperatures, which may explain why it swells between September and April. It also multiplies at a greater rate when the mercury is slightly below core body temperature. This is bad news for anybody who wants to step outside. Rhinovirus likes to make a home in our nostrils, and every time we take a breath of cold air, we’re creating an environment that’s more hospitable for invasion. (In addition to the common cold, the flu virus is wrapped in a lipid coating that toughens in chilly temperatures, making it even more resilient during the winter.)
To make matters worse, our immune system doesn’t work perfectly in colder temperatures. A 2015 study out of Yale discovered that warm nasal cells do an excellent job warding off attacking viruses. But when those nasal cells are cooled — at about 91 degrees Fahrenheit — they become significantly more vulnerable. In this case, cool conditions become a double whammy: The virus’s ability to replicate gets stronger just as your immune response gets weaker.
So does the cold really cause a cold? The answer depends on how you want to slice it. As explained in The Atlantic, if you placed a person inside a sterile room and dropped the temperature, that person won’t get sick from the cold. (A 2002 meta-analysis published in the journal Rhinology dismissed any “cause-and-effect relationship between acute cooling of the body surface and common cold.”) However, if that same person was exposed to rhinovirus and then placed in a cold room, their likelihood of illness could increase.
Incidentally, researchers suggest that this may explain one of the benefits of having a fever: Increasing the body’s temperature creates an environment that’s less rhinovirus-friendly. However, that doesn’t mean that warm weather in general is better for you — the second most common type of cold-causing virus, called non-polio enterovirus, thrives in the summer. Unlike rhinovirus, it likes things hot.
Generally Good Advice
It’s important to remember, however, that temperature is just one of many contributing factors to your health. Lack of sleep, poor hand-washing hygiene, high stress levels, and contact with contaminated surfaces probably share more blame than the weather outside. So while forgetting a stocking cap on a chilly day probably won’t doom you to a week in bed, keeping one handy certainly won’t hurt.