The theory is simple:
How does Covid-19 spread:
* Fomite transmission: touching an affected surface and then touching your face, thats the reason your asked to wash your hands - my take is
that its not guaranteed that the bed sheets, SP or hard surface in the location will be sterile enough to protect you. Mask or no mask once
you touch the face the mask cant protect you from the virus.
* Respiratory particles can reach you directly, in a 1/2 or 1 hrs booking you cant stop this from happening. Respiratory particles last in the air
for 15 mins, all you need to do is remove the mask to catch some air and your at risk.
In all cloth, surgical and N95 ( best ones ) are recommended as a simple barrier to help prevent respiratory droplets from travelling into the air and transmitted onto others ie when the person wearing the mask coughs, sneezes or raises their voice - best know as source control.
It's not a 100 % protection for very close proximity like massage and punting etc IMOH as you still need to maintain some distance and be in an airy environment which is not possible in a room, going to the shower or touching hard surfaces that may have accommodated other punters of which some maybe asymptomatic.