There is so much confusion about whether people should wear masks, why and what kind. Much of the confusion around masks stems from a lack of understanding about the two different functions of masks.
Masks protect the wearer from infection or protect others from infection passed by the wearer. Protecting the wearer requires medical-grade respirator masks, a proper fit, and careful putting on and taking off. They can also be worn to prevent transmission to others, and this is their most important use for the population. Lowering the possibility of one person infecting another has an amazing impact. So a small reduction in those odds results in a huge decrease in deaths. Luckily, blocking transmission outward at the source is much easier.
The main way COVID-19 is spread is via droplets that fly out of our mouths—that includes when we speak, 
not just when we cough or sneeze. This is especially relevant for doctors and nurses who work with sick people all day. Their gear is called “personal protective equipment,” (or PPE). They have stringent requirements for fit to stop ingress; the term for the transmission of outside particles to the wearer. Discussions about masks are about protecting medical workers from ingress.
But the opposite concern also exists: egress, or transmission of particles from the wearer to the outside world. Up until now, less research has been conducted on egress, but controlling it is crucial to stopping the 
person-to-person spread of a disease. Obviously, population compliance becomes very important during a pandemic. Unfortunately, information online doesn’t properly distinguish between ingress and egress, which adds to the confusion.
The good news is that preventing transmission to others through egress is relatively simple. Research shows that even a cotton mask reduces the number of virus particles emitted from our mouths—by as much as 99%.
COVID-19 has been hard to control partly because people can infect others before they themselves display any symptoms—and even if they never develop any illness. Studies show that about half of patients are infected by people who are not coughing or sneezing. Many people have no awareness of the risk they pose to others, because they don’t feel sick themselves, and many never become ill.
If we could just keep our germs from being sent out every time we spoke or coughed, many fewer people would be infected. Masks help us do that. And because we don’t know for sure who’s sick, the only solution is for everyone to wear masks. My mask protects you; your masks protect me.
Models show that if 80 % of people wear masks that are 60 % effective, that will halt the spread of the disease. Many countries have more than 80% of their population wearing masks in public, where most stores deny entry to unmasked customers. More than 30 countries legally require masks in public spaces. Mask use in combination with physical distancing is even more powerful.
A vaccine may take years to come to market. In the meantime, we need to find ways to make our societies function and be safe. Our governments can and should ensure medical workers have everything they need. But ordinary people are not helpless; in fact, we have more power than we realize. Along with keeping our distance and maintaining good hygiene, just wearing a mask will help stop this pandemic in its tracks.