Humidity from masks may help lessen severity of coronavirus infection, say scientists

Not only do facemasks help protect people from getting or spreading the novel coronavirus the humidity created inside masks also hydrate the respiratory tract and benefit the immune system, says a new study.

According to the research, published in the Biophysical Journal, the higher level of humidity in inhaled air could explain why wearing masks is linked to lower disease severity in people infected with the SARS-CoV-2 virus since hydration of the respiratory tract is known to benefit the immune system.

"We found that face masks strongly increase the humidity in the inhaled air and propose that the resulting hydration of the respiratory tract could be responsible for the documented finding that links lower Covid-19 disease severity to wearing a mask," said the study's lead author, Adriaan Bax from the US NIH's National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

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"High levels of humidity have been shown to mitigate the severity of the flu, and it may be applicable to the severity of Covid-19 through a similar mechanism," Bax said.

The scientists said high levels of humidity can limit the spread of a virus to the lungs by promoting mucociliary clearance (MCC) — a defense mechanism that removes mucus and potentially harmful particles within the mucus from the lungs.

They said high humidity can also bolster the immune system by producing special proteins called interferons that fight against viruses while low levels have been shown to impair both MCC and the interferon response.

According to the researchers, this may be one reason why people are more likely to get respiratory infections in cold weather.

In the current study, the scientists tested four common types of masks — an N95 mask, a three-ply disposable surgical mask, a two-ply cotton-polyester mask, and a heavy cotton mask.

They measured the level of humidity by having a volunteer breathe into a sealed steel box.

When the person wore no mask, the water vapour of the exhaled breath filled the box, leading to a rapid increase in humidity inside the box, the study noted.

However, when the person wore a mask, the buildup of humidity inside the box greatly decreased, due to most of the water vapour remaining in the mask, becoming condensed, and being re-inhaled.

The scientists took measurements at three different air temperatures, ranging from about 46 to 98 degrees Fahrenheit.

To ensure no leakage, they said the masks were fitted against the volunteer's face using high-density foam rubber.

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The findings revealed that all four masks increased the level of humidity of inhaled air, but to varying degrees.

At lower temperatures, the researchers said the humidifying effects of all masks greatly increased while thick cotton masks led to the most increased level of humidity at all conditions.

"The increased level of humidity is something most mask-wearers probably felt without being able to recognize, and without realizing that this humidity might actually be good for them," Bax said.

"This research supports the importance of mask-wearing as a simple, yet effective, way to protect the people around us and to protect ourselves from respiratory infection," said NIDDK Director Griffin P Rodgers.