Why do so many people in Japan wear face masks?

If you visit Japan in winter, you might find it strange that so many Japanese people are wearing surgical face masks. You see lots of people with their face covered with white masks on train, on street, in the office, onboard the airplane … basically everywhere. Why do they do that? For most cases, they are either trying to avoid catching any viruses or trying not to pass their cold to others as a caring posture. If you see them in the airplane cabin, chances are that they do so for keeping their throat moisturized. Cabin air is very dry. Its humidity level is as low as 20%. I also [...]