The following information is from David Crowe’s Scientific Information on Masks Against COVID-19. This, and a wealth of incredible information, can be found at his site The Infectious Myth: A Book Project by David Crowe.
A very recent review of the literature that was published in the CDC journal, “Emerging Infectious Diseases” did not find evidence that handwashing or masks were protective against influenza. Masks did not help infected people reduce their risk of infecting others, nor reduce the risk of uninfected people contracting influenza.
“In this review, we did not find evidence to support a protective effect of personal protective measures or environmental measures in reducing influenza transmission…Hand hygiene is a widely used intervention and has been shown to effectively reduce the transmission of gastrointestinal infections and respiratory infections. However, in our systematic review, updating the findings of Wong et al., we did not find evidence of a major effect of hand hygiene on laboratory-confirmed influenza virus transmission…We did not find evidence that surgical-type face masks are effective in reducing laboratory-confirmed influenza transmission, either when worn by infected persons (source control) or by persons in the general community to reduce their susceptibility…It is essential to note that the mechanisms of person-to-person transmission in the community have not been fully determined. Controversy remains over the role of transmission through fine-particle aerosols.”
Xiao J et al. Nonpharmaceutical Measures for Pandemic Influenza in Nonhealthcare Settings-Personal Protective and Environmental Measures. Emerg Infect Dis. 2020 May 17; 26(5).
A Korean study put masks on COVID-19 infected people and did not reduce the transmission of viral RNA when patients coughed with a mask on.
“Neither surgical nor cotton masks effectively filtered SARS–CoV-2 during coughs by infected patients.”
Bae S et al. Effectiveness of Surgical and Cotton Masks in Blocking SARS-CoV-2: A Controlled Comparison in 4 Patients. Ann Intern Med. 2020 Apr 6.