When health care workers wear surgical masks, there’s good evidence it limits the spread of respiratory viral infections in hospitals. But there is no clear evidence that surgical masks protect members of the public from getting or passing on these sorts of infections—most likely because of incorrect use. For cloth masks worn by the public, the picture is even murkier.
Surgical masks are made up of several layers of non-woven plastic and can effectively filter very small particles, such as droplets of SARS-CoV-2 (the virus that causes COVID-19). The masks typically contain an external waterproof layer and an internal absorbent layer.