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That Annoying Moisture in Your Mask? It Might Prevent COVID Infection

February 18, 2021

Built-up humidity inside your mask, as uncomfortable as it might feel, can actually fight respiratory diseases such as COVID-19, according to researchers at the National Institutes of Health.

The humidity produced by inhaled air might explain why masks are associated with less severe cases of COVID-19. A hydrated respiratory tract, say the researchers, helps the immune system by producing virus-fighting proteins called interferons. And mucociliary clearance removes mucus from the lungs, taking potentially harmful particles with it.

“High levels of humidity have been shown to mitigate severity of the flu,” says Adrian Bax, an NIH Distinguished Investigator, “and it may be applicable to severity of COVID-19 through a similar mechanism.”

The study tested four familiar masks, including an N95, a three-ply disposable surgical mask, a two-ply polyester mask and a heavy cotton mask. The researchers measured humidity levels of volunteers who breathed into a sealed box. (Above, Dr. Joseph Courtney of the National Institute of Diabetes and Digestive and Kidney Diseases breathes into the box.)

Maskless volunteers filled the box with water vapor from their exhaled breath. Masked volunteers, however, retained much of the water vapor from their exhaled breath, then inhaled it as it condensed. Each of the four masks increased the humidity of inhaled air, particularly at lower temperatures. The thick cotton mask produced the highest increase in humidity.

The study, published in Biophysical Journal, also found that low humidity levels affected both interferon response and mucociliary clearance, leaving the body vulnerable to infection. It could also explain why people are more susceptible to respiratory infections in lower temperatures.

“It’s as important as ever to wash your hands, wear a mask and don’t touch your face,” said Keith Grant, APRN, head of infectious disease for Hartford HealthCare. “Those are still the basic ways to avoid COVID-19 infection.”