From researchers at the University of Hong Kong, whos studied 14 randomized controlled trials of various factors in virus transmission:
"Although mechanistic studies support the potential effect of hand hygiene or face masks, evidence from 14 randomized controlled trials of these measures did not support a substantial effect on transmission of laboratory-confirmed influenza."
"In pooled analysis, we found no significant reduction in influenza transmission with the use of face masks."
"There is limited evidence for their effectiveness in preventing influenza virus transmission either when worn by the infected person for source control or when worn by uninfected persons to reduce exposure. Our systematic review found no significant effect of face masks on transmission of laboratory-confirmed influenza."
Link: RCTs show masks don't work