If you feel confused about whether people should wear masks and why and what kind, you’re not alone. COVID-19 is a novel disease and we’re learning new things about it every day. However, much of the confusion around masks stems from the conflation of two very different functions of masks.

Masks can be worn to protect the wearer from getting infected, or masks can be worn to protect others from being infected by the wearer. Protecting the wearer is difficult: It requires medical-grade respirator masks, a proper fit, and careful putting on and taking off. But masks can also be worn to prevent transmission to others, and this is their most important use for society. If we lower the likelihood of one person’s infecting another, the impact is exponential, so even a small reduction in those odds results in a huge decrease in deaths. Luckily, blocking transmission outward at the source is much easier. It can be accomplished with something as simple as a cloth mask.

A key transmission route of COVID-19 is via droplets that fly out of our mouths—that includes when we speak, not just when we cough or sneeze. A portion of these droplets quickly evaporate, becoming tiny particles whose inhalation by those nearby is hard to prevent. This is especially relevant for doctors and nurses who work with sick people all day. Medical workers are also at risk from procedures such as intubation, which generate very tiny particles that can float around possibly for hours.
 
The good news is that preventing transmission to others is relatively easy. Research shows that even a cotton mask dramatically reduces the number of virus particles emitted from our mouths—by as much as 99 percent. This reduction provides two huge benefits. Fewer virus particles mean that people have a better chance of avoiding infection, and if they are infected, the lower viral-exposure load may give them a better chance of contracting only a mild illness.
 
Masks help us keep those droplets from being sprayed every time we speak or cough. And because we don’t know for sure who’s sick, the only solution is for everyone to wear masks. This eventually benefits the wearer because fewer droplets mean we’re all less likely to get sick. My mask protects you; your masks protect me.