Multiple lines of evidence back the use of face masks to protect against the coronavirus, although some uncertainty remains as to how effective mask interventions are in preventing spread in the community.
Lab tests, for example, show that certain masks and N95 respirators can partially block exhaled respiratory droplets or aerosols, which are thought to be the primary ways the virus spreads.
Observational studies, while limited, have generally found mask-wearing to be associated with a reduced risk of contracting the virus or fewer COVID-19 cases in a community.
A few randomized controlled trials have found that providing free masks and encouraging people to wear them results in a small to moderate reduction in transmission, although these results have not always been statistically significant.
Masks should not be viewed as foolproof, as no mask is thought to offer complete protection to the wearer or to others. The Centers for Disease Control and Prevention recommends that people wear the most protective mask that fits well and can be worn consistently. Loosely woven cloth masks are the least protective. Layered, tightly woven cloth masks offer more protection, while well-fitting surgical masks and KN95 respirators provide even more protection and N95 respirators are the most protective.