WHO on masks [www.who.int
"If you are healthy, you only need to wear a mask if you are taking care of a person with suspected 2019-nCoV infection.
Wear a mask if you are coughing or sneezing."
Before putting on a mask, clean hands with alcohol-based hand rub or soap and water.
Cover mouth and nose with mask and make sure there are no gaps between your face and the mask.
Avoid touching the mask while using it; if you do, clean your hands with alcohol-based hand rub or soap and water.
Replace the mask with a new one as soon as it is damp and do not re-use single-use masks.
To remove the mask: remove it from behind (do not touch the front of mask); discard immediately in a closed bin; clean hands with alcohol-based hand rub or soap and water.
I would guess that few people have a close fitting mask covering mouth and nose ,that few take it off as carefully as they should and that many walk about with a damp warm mask where bugs will linger and breed . And that many wearing a mask will induce a false sense of security and that as a consequence they will not keep their distance from others as they should .