evidence: "It’s true that masks are most effective when everyone around you is wearing them. If someone is infected with COVID-19 and doesn’t know it, their mask is like putting a thumb over the end of a hose, preventing the virus from spewing," says Jaimie Meyer, an infectious disease physician at Yale Medicine. [...] To be effective, the CDC emphasizes masks must be worn consistently. Some people in areas with high transmission may think they are safe without a mask indoors when they remain more than six feet from others in the room. But it’s a misconception that keeping your distance inside reduces your risk of exposure completely, says Linsey Marr, professor of engineering at Virginia Tech and an expert on viral transmission. It’s true that viral particles are concentrated closest to an infected individual, she says, but just as cigarette smoke eventually spreads throughout a room, so, too, does the coronavirus. [...] Anyone not currently wearing a mask still should keep it at the ready, experts say.