A new “scientific brief” added to CDC’s website on Nov. 10 recommends the community use of non-valved, multilayered cloth masks to control the spread of COVID-19. According to the agency, masks are primarily intended as source controls to reduce the emission of potentially virus-laden respiratory droplets generated when people cough, sneeze, sing, talk, or breathe. Cloth masks also provide some personal protection for wearers, CDC states. The agency stresses that the community benefit of the use of cloth masks to prevent transmission of SARS-CoV-2 is due to a combination of these effects.

“The relationship between source control and personal protection is likely complementary and possibly synergistic, so that individual benefit increases with increasing community mask use,” CDC’s webpage states.

The page lists observational and epidemiological studies that examine the “real-world” effectiveness of community masking. One study of two symptomatic hairstylists who interacted with 139 clients for an average of 15 minutes each over eight days found that none of the 67 clients who consented to testing developed an infection. The stylists and clients all wore masks as required by local ordinance and company policy.

Seven studies concerning a variety of communities—including a Massachusetts hospital system, the German city of Jena, and a panel of 15 U.S. states plus Washington, D.C.— “confirmed the benefit of universal masking in community-level analyses,” CDC says.

CDC states that further research is needed to expand the evidence base for the protective effect of cloth masks, particularly to determine the most effective combinations of materials.