Here's a summary of the latest research (randomized clinical trials) from Cochrane, in studies including hundreds of thousands of people: Cochrane Library has reviewed these studies: https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006207.pub6/full?highlightAbstract=covid%7Cmask "...We included 12 trials (10 cluster‐RCTs) comparing medical/surgical masks versus no masks to prevent the spread of viral respiratory illness (two trials with healthcare workers and 10 in the comm