Yeah, right: Re-breathing in all that bacteria that your lungs just exhaled is a "healthy" practice that boosts your immune system. Who at the NIH spearheaded and signed their names to this study?
-NW

Sounds gross, but a moist mask is good for you. Study shows that re-inhaling the air in your mask hydrates your lungs and boosts the immune system
Nick Beare | healthing.ca
February 16, 2021

[snip]

A new study from the National Institutes of Health is suggesting yet another reason why wearing a mask works. Not only are face coverings effective in preventing the spread of COVID-19, but masks may also lower the severity of the virus.

Researchers in the NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) are saying that the increase in humidity in the air that the mask-wearer breathes in could help explain why wearing masks has been linked to lower disease severity in people infected with COVID-19, because hydration of the respiratory tract is known to benefit the immune system.