Laboratory tests of surgical and N95 masks by researchers at the University of California, Davis, show that they do cut down the amount of aerosolized particles emitted during breathing, talking and coughing. Tests of homemade cloth face coverings, however, show that the fabric itself releases a large amount of fibers into the air, underscoring the importance of washing them. The work is published today (Sept. 24) in Scientific Reports.
I don a new surgical mask for every session and have been making patients do the same because I don't have confidence they're cleaning their own masks regularly. Besides, many of their masks look ratty and don't fit well.