How Masks protect the wearer even if others nearby are not wearing masks.

If I’m the only person wearing a mask in a store or other indoor location, am I really protected from infection?

It’s true that masks work best when everyone in the room is wearing one. That’s because when an infected person wears a mask, a large percentage of their exhaled infectious particles are trapped, stopping viral spread at the source. And when fewer viral particles are floating around the room, the masks others are wearing would likely block those that have escaped.

But there is also plenty of evidence showing that masks protect the wearer even when others around them are mask-free. The amount of protection depends on the quality of the mask and how well it fits. During a hotel outbreak in Switzerland, for instance, several employees and a guest who tested positive for the coronavirus were wearing only face shields (with no masks); those who wore masks were not infected. And a Tennessee study found that communities with mask mandates had lower hospitalization rates than areas where masks weren’t required.

“Health care workers, scientists who work with nasty pathogens, and workers who may be exposed to hazardous airborne particles on the job rely on specialized masks like N95s for protection, so we know that properly fitted, high-efficiency masks work,” said Linsey Marr, a Virginia Tech engineering professor and one of the world’s leading experts on viral transmission.

A number of laboratory studies have also documented that a mask protects the person who is wearing it, though the level of that protection can vary depending on the type of mask, the material it’s made from, the experimental setup and how particle exposure was measured. ...

But the bottom line of all the studies is that a mask reduces the potential exposure of the person wearing it. Here are some of the findings. ...