Actually, the mask isn’t to protect the wearer, it’s to keep the wearer from spreading their own germs. That’s why doctors and dentists wear masks. Your dentist isn’t afraid of catching cavities from you; he doesn’t want to breathe his own germs into your open mouth.
“It may interest you to know that I have made a lifelong study of lemmings, just as you have made a lifelong study of people. Like you, I have found but one thing about my subject which I do not understand.”“And what is that?” asked the lemming.“I don’t understand,” said the scientist, “why you lemmings all rush down to the sea and drown yourselves.”“How curious,” said the lemming. “The one thing I don’t understand is why you human beings don’t.”
— from “Interview with a Lemming,” by James Thurber
“You” is a pronoun.