what is the point of the mouth mask?

In China, pollution. In Japan, they believe it helps to prevent of give a cold,even though the cold virus is small

enough to pass right through the mask. It does help with dust / pollens.

All the time? But I'm a Japanese and do not wear a mask at all.

I think you have seen just a fraction of people. But I've heard that many Chinese wear a mask in cities because of pollution.

In China it's because of the Pollution, China is the home of many industries and factories.

In Japan People want to avoid getting sick or passing the Virus to other people, It's Cold in Japan.

It doesn't do anything for pollution. It was originally used as a mean to prevent the spread of diseases such as colds and flu. It is being considerate of others for someone who is still ill but out and about to wear these mask so they do not infect others around them.

Many reasons - keep colds etc to themselves, prevent sickness, fashion statement, and of course pollution in china from experience its bad

1. Virus

It may not shield virus or bacteria off, but it helps keep the lining of your nose, throat and bronchial tubes at the right humidity. If kept at the right level, the risk of getting ill will get substantially reduced.

2. Allergy to pollen

If you are allergic to pollen, it is effective to prevent runny nose or asthma.

Paranoia.

They are effective in reducing particulates. They are totally useless at filtering pollutant gases or viruses. However (like green tea) if someone claims they are healthy, everyone wants one.

Probably just being a bit to paranoid lol