Is it true that going outside in the cold with wet hair will make you sick?

Many of us have heard the warning: Don’t go outside in the cold with wet hair — or you’ll catch your death.

It stems from the fear that getting too cold can predispose us to illness.

There’s not much truth to it. But it may not be completely false, either.

The common cold, flu and other respiratory diseases, including covid-19, are caused by viruses. Some sinus infections are caused by bacteria. These germs are usually spread by breathing in respiratory droplets and particles from people who are sick, eating or drinking after them, or touching contaminated surfaces and then touching your eyes, nose or mouth.

“You can’t get a cold just from going out in the cold,” said Sean O’Leary, chair of the Committee on Infectious Diseases for the American Academy of Pediatrics.

Winter weather can, however, create a more agreeable environment for germs — both outside and inside our bodies. Some research has suggested that cold temperatures may help the influenza virus to survive better, for example.

Cold temperatures can also affect our immune systems, leaving us more susceptible when exposed to germs.

A 2018 study discovered that the area just inside the tip of each nostril contains receptors that can detect bacteria that are inhaled. The immune system then sends out a swarm of tiny bubbles, known as extracellular vesicles, into the mucus in the nose to kill the bacteria before they have a chance to cause an infection. In a 2022 study, researchers found that a similar process occurs with viruses — and that, most important, when the nose gets cold, its ability to perform this function may be hindered.

The totality of the research shows that “our susceptibility to viral infection roughly doubles as you drop in temperature, even by only 5 degrees” Celsius, said Benjamin Bleier, director of otolaryngology translational research at Massachusetts Eye and Ear, who was the senior author of both studies.

Hypothermia — a significant drop in body temperature caused by prolonged exposure to extreme cold — can also suppress the immune system.

“I wouldn’t worry so much about going outside with wet hair,” O’Leary said. “I would worry about making sure you’re protected from the things we know can be very severe,” particularly by getting vaccinated against the coronavirus, the influenza virus and the respiratory syncytial virus or RSV.

What else you should to know:

Some people may be more likely to get sick in the winter, but not because they are spending time outside in the cold. In some cases, it may be the opposite, experts say.

“During the winter, people gather together in closed spaces,” where there is poor ventilation, said Monica Gandhi, an infectious-disease expert at the University of California at San Francisco. This proximity to family members and friends during cold and flu season “increases exposure to viruses from interaction with others,” she said.

You cannot get sick simply by going outside in the cold with wet hair; you must come into contact with a cold or flu virus, for instance. The cold temperatures, however, may make you more susceptible to an infection when you are exposed to certain germs.

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