its required in japan that you wear a medical mask if your sick or something along those lines
also its people in a chatroom telling qt japanese grills to say funny ****
No it's not required at home, if you have a cold you are expected to wear one at public areas or your work, however it's not regulated by any law. It's common that people wear them outside during flue season etc even if not sick though.
Lots of people in the bigger cities also wear them in order to lower the amout of poulution they inhale.
Also underaged people use them sometimes since they may not show there faces in public media without parents consent.