One mask or even a dozen face masks are pointless

You have to throw away the mask and get a new one when:

-The mask gets moist from your breath. Moisture wicks in the virus and actually promotes infection. It takes about 10 minutes for the mask to get bad.

-You touch the mask with your hands and contaminate it. You wear the mask by grabbing on the straps. First you wash your hands, you put the mask on and wash your hands again.

-Someone coughs or sneezes at you. You need to replace the mask ASAP.

Also, if you have a beard or even a stubble, the mask is useless. Clean shaven is the only way to go.