This is how diseases is spread. https://www.youtube.com/watch?v=MeCGTRh27Tg It is not from you projectile spitting in someone's face while talking to them. It is simply your breath. An aerosol gas leeching around. Imagine a grocery store with hundreds of people in it. It is a literal stew of everyone's breath swirling around. You have to stop the moisture breath from getting out to prevent disease spread.