Comment by Raphmedia

Masks in Japan are based on the desire of Japaneses not to infect others and not to spread their own germs. They won't filter the air coming in or out, but they'll catch a sneeze and a cough. They also make it so you don't put your fingers in your mouth or nose. It's the sick that wear them. You barely see them elsewhere because the idea of "wear something uncomfortable for the sake of others" is a hard sell in the west.