Don’t know about percentage of filtered droplets/aerosol in both directions, but I would guess the reasons include:
1. A mask doesn’t protect your eyes
2. You are likely to touch contaminated outer surface of your mask (and then touch your mouth, scratch your eye etc and get infected), but other people probably won’t touch the inner surface of your mask.
Don’t know about percentage of filtered droplets/aerosol in both directions, but I would guess the reasons include:
1. A mask doesn’t protect your eyes
2. You are likely to touch contaminated outer surface of your mask (and then touch your mouth, scratch your eye etc and get infected), but other people probably won’t touch the inner surface of your mask.