A new study, conducted by researchers from the National Institutes of Health, U.S., suggests that there is another positive effect of wearing masks: the humidity created inside the mask may help reduce COVID-19 severity.

In the study, the scientists found that face masks significantly increase the humidity levels in the air that the person wearing the mask breathes in. The researchers suggest that this could help explain why wearing masks has been linked to lower disease severity in people infected with SARS-CoV-2.

The researchers tested 4 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.

The analysis of the received data showed that all masks increased the level of humidity of inhaled air. At lower temperatures, the humidity inside of all masks greatly increased. But the thick cotton mask led to the most increased level of humidity at all tested temperatures (from about 46 to 98 degrees Fahrenheit).