Unexpected masking benefits

Foggy glasses have frustrated people wearing masks during the coronavirus pandemic, but they might also signify a benefit of masking: humidity.

Though the primary goal of masks is to control transmission, according to the authors of a new study, wearing one may make symptoms less severe when people do contract diseases. Researchers for the National Institutes of Health on Friday published a report in the Biophysical Journal saying the humidity inside a mask may help the body’s respiratory system naturally fend off diseases like COVID-19. The study did not investigate whether masks prevent transmission.

“High levels of humidity have been shown to mitigate severity of the flu, and it may be applicable to severity of COVID-19 through a similar mechanism,” lead author Adriaan Bax said.

The researchers first measured how much humidity people build up inside masks. They gave test subjects four different types of face coverings ranging from N95 masks to simple, single-layer cotton masks. Test subjects breathed directly into a metal box that measured humidity. Without a mask, test subjects increased the humidity within the metal box a great deal. But that amount lessened when test subjects donned masks. Cotton face coverings held in the most humidity, but all of them helped at least some, according to the report. The experiment demonstrated some of the moisture test subjects breathed out remained in their mask, making their next breath more humid.

Nearly a year into the coronavirus pandemic, scientists probably didn’t need to convince the public that breathing through a mask leads to warmer, moister air. But the National Institutes of Health team also suggested increased humidity might explain why masks have been associated with less severe cases of COVID-19. They speculated high humidity could stimulate hair-like cilia in the lungs to begin removing debris from the respiratory system. The body’s cilia help move mucus, and the harmful particles it carries, from the lungs. Overactive cilia could help the body clear the disease from the lungs more easily. High humidity, researchers observed, also helps the body create more immune system proteins called interferons.

The U.S. Centers for Disease Control and Prevention issued new guidelines on Feb. 13 urging the public to wear masks that have multiple layers of material and fit snugly against the face. There is debate about whether the virus can transmit through airborne particles, which could limit masks’ effectiveness. Face coverings can block larger respiratory droplets carrying the disease.