In some states and major cities, it's now mandatory to wear a mask in public to prevent the spread of COVID-19. That mask could be anything from a handkerchief to a designer cotton mask to a full-blown N95 respirator, so long as you have something between your mouth and nose and the world around...science.slashdot.org
"Why? Because a mask with a valve may protect you from some pathogens in the air, but it doesn't protect the people around you from your own breath."
Astonishing ! I can't believe that's true:
https://edition.cnn.com/2020/05/07/politics/axl-rose-steve-mnuchin/index.html (last paragraph)
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