The advice on widespread face mask use to protect against covid-19 varies wildly, but there is some evidence that they stop sick people spreading the virus
Source:
https://www.newscientist.com/article/2240288-do-face-masks-work-against-the-coronavirus-and-should-you-wear-one/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home