On top of providing some limited protection of the wearer, it also works like herd immunity in that if everyone wears them, then those that don’t yet know they’re sick are reducing their spread.

At the moment because of the misinformation people wearing masks are being mocked and chided in public and its really unhelpful. Especially since there are immune compromised individuals and individuals with other conditions that really need to take every precaution they can, including that 10% reduction a surgical mask may give them.

My layman's understanding is that any barrier will stop some percent of most things. In the case of small, airborne particles, this stopped percentage of already-dry, floating material is very small. That means inhaling through them is relatively ineffective at stopping you from inhaling the particles.

When you exhale it is more wet and the moisture causes the barrier to catch more of the airborne particles. The barrier also catches any more-solid material that would otherwise land elsewhere, providing a mechanism for the particle to spread.

This means the net gain for wearing them to keep from catching the disease is relatively small compared to the gain by wearing them to prevent the spread if you may have been exposed.

Would you agree a fair corollary of that is: if everyone wears masks then spreading of the contagion would be reduced considerably.

It may primarily be about preventing spread from those infected, but that's still super helpful.

I would agree if everyone exposed wore masks the spread of this contagion would be reduced considerably.

Logically, I might extend it to everyone wearing masks would considerably reduce the spread of exhaled contagions. This might first be encouraged in high population density areas, like parts of Asia, and first need to be integrated with fashion[0] to have any chance of broad success. I suspect it will never be a preference everywhere barring some sort of serious consequence (like death) for not wearing the mask.

In this situation, I think the most important thing is to know that normally available or homemade masks are helpful for presenting the spread of the disease. The more expensive masks are better but in this instance, not better in a meaningful way for the average person. The current supplies should be saved for those at-higher-risk populations like medical staff.

[0]: https://www.pinterest.ca/charmed4evr/fashionable-surgical-fa...

You must also remember about disposing of the mask properly. E.g. don’t put used masks in your pockets.