Growing up in Sri Lanka, it was an article of faith with my mother (and the mothers of many of my friends) that after a shower, we should not go outside while our hair was still wet because that increased the risk of us catching a cold or getting a chill. If we happened to get caught in the rain, we were told to quickly dry ourselves thoroughly so that we did not catch a cold. But Sri Lanka is a tropical country where what is considered ‘cold’ would be like a balmy summer day in the US. Furthermore houses have very open architecture with open windows and doors so that air is freely circulating and hence there is little difference between ‘inside’ and ‘outside’ except that inside one had a roof over one’s head. Hence these restrictions made no sense. But given the power of confirmation bias, it was always easy to find such a cause to blame whenever one caught a cold.
In the US, children are told to dress warmly when going out in cold weather so that they too will not catch a cold. So does wet hair or ambient cold increase the chances of catching cold? This article looks at the relationship between being cold and wet and catching a cold and, as with so many things, it is a little complicated.
Many of us have heard: “Don’t go outside without a coat; you’ll catch a cold.”
That’s not exactly true. As with many things, the reality is more complicated. Here’s the distinction: Being cold isn’t why you get a cold. But it is true that cold weather makes it easier to get the cold or flu. It is still too early to tell how weather impacts the COVID-19 virus, but scientists are starting to think it behaves differently than cold and flu viruses.
Many viruses, including rhinovirus – the usual culprit in the common cold – and influenza, remain infectious longer and replicate faster in colder temperatures. That’s why these viruses spread more easily in winter. Wearing a heavy coat won’t necessarily make a difference.
More specifically, cold weather can change the outer membrane of the influenza virus; it makes the membrane more solid and rubbery. Scientists believe that the rubbery coating makes person-to-person transmission of the virus easier.
It’s not just cold winter air that causes a problem. Air that is dry in addition to cold has been linked to flu outbreaks. A National Institutes of Health study suggests that dry winter air further helps the influenza virus to remain infectious longer.
In addition, cold weather dries out your eyes and the mucous membranes in your nose and throat. Because viruses that cause colds and flu are typically inhaled, the virus can attach more easily to these impaired, dried-out passages.
So there is a bit of truth in the idea that ambient cold can lead to one being more likely to catch a cold but that is not due to the individual being cold but what happens with the virus in cold temperatures.
I suspect that these beliefs arose because of the external conditions that do exist in the temperate climates then got transmitted all over the world and even to the tropics where those conditions do not apply.