Masks reduce spread of the virus by already infected people. They work because even people who don't even know they are sick are wearing them from the beginning to the end of their infection. When it comes to exponential growth it doesn't matter if the masks reduce infection rate by 10%, 1% or even 0.1%. Alternatively, even if masks don't work physically there is a psychological component to wearing masks that can reduce the infection rate by reminding people that there is a virus out there and as long as you are wearing the mask you should be extra careful.
There's not much evidence to support anything in your comment.
If masks were so effective it would be easy to find that benefit in any of the good quality trials that have been run, and we don't see that benefit. To see any benefit of mask wearing we have to drop the quality of evidence right down.
One thing often missing from these discussions is the concept of "number needed to treat". How many people need to wear a mask to prevent one additional infection?
> Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small. Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms, and assuming a risk reduction of 40% for wearing facemask, 200000 people would need to wear facemasks to prevent one new infection per week in the current epidemiological situation.
