Face shields have been recommended for use by hairdressers, and are worn by teachers in some schools. But plastic face shields are not effective at stopping airborne droplets from escaping from an infected person’s mouth, according to a study in Japan.
Computer simulations showed that almost 100% of droplets under five micrometres (released when people talk and breathe) got past the visor, along with 50% of the larger droplets (over 50 micrometres) that are released with coughs and sneezes. The World Health Organisation says the shields, which do not completely cover the face, should be used with a mask. (The Week, 3 October 2020)
My comment: I posted the above wondering what the point of a face shield would be if you had to wear a mask with it. The reader is probably thinking the same. Why don’t they test these things before they sell them?