The CDC is recommending that people wear face coverings or cloth masks if they go out in public

• The CDC is recommending - but not requiring - that people cover their faces if they have to go out in public as the coronavirus spreads across the US.
• There isn't much good evidence that masks help prevent infection from spreading in a population, except when you put them on the people who are already sick.
• There are also risks associated with wearing a homemade mask: you might just be turning your scarf into a virus-catcher.
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If you must go out, cover up, according to new recommendations from the US Centers for Disease Control and Prevention on how to curb spread of the novel coronavirus.

The recommendations, announced by President Trump on Friday, come as emerging evidence suggests people can transmit the coronavirus to others before they ever know they've been infected.

"In light of these studies, the CDC is advising the use of non-medical cloth face covering as an additional voluntary public health measure" President Trump said. "So it's voluntary, you don't have to do it ... I don't think I'm going to be doing it."

It's quite different from recommendations during the early days of the pandemic, when public health experts at the CDC said the agency did not "recommend the use of face masks for the general public," and the US surgeon general urged Americans to stop buying masks.

Scientists still don't have solid evidence that masks work well at preventing infectious disease outbreaks, especially the homemade kind. Masks may do a little bit to help sick people from spreading their infections to others, and are certainly useful for caregivers and healthcare workers who are exposed to lots of coronavirus particles as they care for sick patients.

For this reason, and because masks are in such short supply, public health experts have stressed that surgical masks should be saved chiefly for healthcare workers (and caretakers) who are more exposed to the virus than the general public.

Experts are concerned that homemade face coverings don't help and could even be harmful

Generally, health experts are still skeptical that masks will do a lot to prevent more people from getting sick. It's true that some people may shed coronavirus before they show symptoms, unwittingly infecting others with COVID-19 by coughing, spitting, sputtering, or just breathing on them.

But this is not the main way the virus is transmitted.

"We have to look at is what is the main driver of this pandemic," World Health Organization Executive Director of Health Emergencies, Mike Ryan, told reporters on a call Friday. "We still believe the main driver of this pandemic is symptomatic individuals coughing or sneezing or contaminating surfaces or contaminating other individuals. Breaking that chain means ensuring that infected individuals are diagnosed and isolated, their contacts are traced and tracked and quarantined, and that people are cared for very quickly."

What's more, textile experts remain concerned that homemade face coverings, which are crafted from woven fabrics built by porous yarns, may not do nearly as much to protect people as surgical masks, which are usually manufactured from nonwoven filtration fabrics, and may even be designed to trap virus particles inside. Clothes and scarves don't do that.

"Homemade masks may give more peace of mind than actual physical protection," textile engineer Emiel DenHartog, Associate Director of the Textile Protection and Comfort Center at North Carolina State University, told Business Insider in an email. "In personal protection, it is generally not true that anything is better than nothing."

Ben Cowling, a professor of epidemiology and a mask researcher at the University of Hong Kong's School of Public Health, who himself wears a mask when he goes out in public, said that staying home is still a better way to stay virus-free.

"Social distancing would definitely be the best," Cowling told Business Insider. "I mean, if everybody stays in their home, then there's no way for the virus to spread."

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