Depending on where you live, you might be seeing masked joggers and cyclists on the streets of your neighborhood. Or you might have gone for a run yourself, mask-free, and been heckled to mask up. At this point, most thoughtful people wear masks indoors in public and outdoors in crowded situations, but wearing a mask when you’re outdoors and alone — or far away from anyone else — has become a frontier of intense debate.

U.S. presidential candidate Joe Biden added to the confusion when he recently called for a national mask mandate. In no uncertain terms, he said it could save 40,000 lives over the next three months if everyone wore a mask "outside.”

But that’s not what the experts say. For one thing, there’s overwhelming evidence that the virus is being transmitted primarily indoors. That’s why director of the National Institute of Allergy and Infectious Diseases Tony Fauci has said he and his wife pull their masks down to their chins when they jog outside — he only pulls it back over his nose and mouth if he has to pass someone.