Actually, anyone who lives in a residential or commercial building in which the return air comes from within the building is, unknown to that person and to others who are not informed, breathing stale used air.

If that air is filtered but if the filter was not efficiently changed, that makes matters worse because added to the stale air are fungus and other micro-dudes who sprout on the filter, germinate and then multiply.

Most of the air systems use is return air. Even in cars this happens when one presses the button that shows a circular arrow.

It is only where all the air comes from the outside to be heated or cooled, does the person get full fresh air and the filter must be changed frequently which is expensive which discourages changing it.

This means that most people using machine cooled or heated air, are using masks which are the machines and the concrete or wooden building.

Another bit of information which may be overlooked is that in the Muslim countries where the laws about women’s coverings are enforced, many women are masked for several hours daily.

When there was the vast migration to Europe from the Islamic regions, Europeans did not like the mask of the women. For one thing they were concerned with masks covering faces which foil the ability to identify persons committing crimes. But the situation with mask now which is global, gives us some idea of what the Muslim women endure day to day.

Despite the reasons for the Islamic masking of women, one basis for it which made sense in previous times, was the protection from lung damage in dust storms in the Sahara Desert. Both males and females had to wear it to prevent sand particles from getting into the lung. But now it is used for who knows what reasons!