High-speed dental drills can send saliva and viral particles into the air where they can be suspended for hours on end.

It follows warnings that viral particles are too small to be trapped by the filters in most airconditioning systems.

Laboratory tests have shown that infected cells seems to produce viral particles faster.

And try not to cry because tears or droplets from a runny nose might mingle with viral particles.

Yet viral particles are hardy enough to remain active for a while outside of the host, with some staying infectious for hours, days or weeks.