The Center for Disease Control and Prevention has officially recommended that people wear cloth or fabric face coverings when entering public spaces like grocery stores or public transit stations. This is mostly to prevent those who have the virus—or those who are infected without knowing it—from spreading the sickness to others.
The guidelines are vague aside from specifying that "cloth face coverings fashioned from household items or made at home from common materials at low cost can be used as an additional, voluntary public health measure."
President Trump stated that wearing masks is voluntary and that he has no intention of doing so. For weeks, U.S. health authorities discouraged Americans from wearing masks, but research has led officials to alter their stance on the matter.
It is slowly becoming impossible to determine healthy individuals from asymptomatic individuals without a formal test—which means that wearing a mask might be the only way to prevent the spread of the virus.
The mask does not have to be professional-grade to offer some sort of benefit. The CDC recommends that the public construct masks made from cloth at home so as to preserve N95 or medical masks for doctors and nurses who need it amidst a shortage of supplies.
While the European Centre for Disease Prevention and Control still discourages the use of masks, some European countries like Austria and the Czech Republic have told residents to cover their mouths and noses before entering stores.