How to Use Masks during the Coronavirus Pandemic

Scientific American

Randomized controlled studies have shown mask-wearing is indeed effective against the flu, but such trials do not currently exist for masks and the coronavirus. “The evidence isn’t always as perfect as we would like it to be,” Koehler says. “Based on the aerosol science, we know that the masks are going to help reduce the transmission of these particles. Can it be 100 percent effective? Maybe not. But can it help? I think so.”