As the CDC has been telling us since last spring, cloth masks work primarily by reducing our risk of infecting others. Since mask mandates tend to get imposed only during surges in the virus, the evidence for face masks is not as strong as we would like but it sure does make sense that cloth masks do protect others from spray coming from our mouths and our coughing.

Yet we should emphasize that, as shown in an 18 November article from the Annals of Internal Medicine, there is little evidence that cloth or disposable masks provide much protection for the person wearing them. Thus, if you have a loved one who is more vulnerable to COVID19, you should consider buying him or her a face shield and maybe some gloves or a designed-to-purpose mask instead of a homemade cloth mask. These items do protect the person who is wearing them.

Direct measures to protect the vulnerable should be a key focus for our coronavirus containment efforts. Viruses invade through our mucosa: normally via our eyes and nose. Face shields protect our eyes from spray and help prevent us from touching or rubbing our eyes and nose. Face masks, especially when they become moist, do not provide these protections.

There is no silver bullet and neither face shields nor cloth masks are very effective at protecting us from microscopic droplets, called aerosol, that can float throughout a room after a cough. It is not yet clear if COVID19 is spread via aerosol but, if it is, then N95 or non-medical-grade high-efficiency masks would help, and these can be worn with face shields.

Thanks much!