What is the true reason that masks are worn in Japanese videos?

Now I've heard many things. Such as, it is illegal to show your face on the internet. I'm not sure if it's true though because, well, i don't know. That's what I think. I always believed it was to prevent stalkers or to conceal their identity in case colleagues or classmates etc etc see them. Can anyone from Japan or anyone knowledgeable about this information tell me?What is the true reason that masks are worn in Japanese videos?
Most people who wear masks in public do so for two reasons.1) They have a cold or flu and don't want to infect others. 2) They are sensitive to car / bus fumes and try to filter it out.This started long before any flu's you see on the news.What is the true reason that masks are worn in Japanese videos?
If you are talking about those armature otaku dancing videos uploaded on youtube, that's because they are being shy. The concerns that you mentioned also are mostly true. Not all Japanese are like that, though. Cell-phone using kogals, for example, don't mind showing their faces to the public at all.





And no, there isn't such a ridiculous law that prohibits showing your face on the internet.
It started with the avian flu and now the swine flu. People in Tokyo think wearing a surgical mask will keep them safe from infectious disease.