|| Update : March 31

A few months ago, it may have seemed silly to wear a face mask during a trip to the grocery store. And in fact, the mainline public health message in the U.S. from the Centers for Disease Control and Prevention has been that most people don't need to wear masks.

But as cases of the coronavirus have skyrocketed, there's new thinking about the benefits that masks could offer in slowing the spread. The CDC says it is now reviewing its policy and may be considering a recommendation to encourage broader use.

"Face masks will be most effective at slowing the spread of SARS-CoV-2 if they are widely used, because they may help prevent people who are asymptomatically infected from transmitting the disease unknowingly," Gottlieb wrote. Gottlieb points to South Korea and Hong Kong — two places that were shown to manage their outbreaks successfully and where face masks are used widely.

The argument for broadening the use of face masks is based on what scientists have learned about asymptomatic spread during this pandemic.

It turns out that many people who are infected with the virus have no symptoms — or only mild symptoms.

What this means is that there's no good way to know who's infected. If you're trying to be responsible when you go out in public, you may not even know that you're sick and may be inadvertently shedding the virus every time you talk with someone, such as a grocery store clerk.

"If these asymptomatic people could wear face masks, then it could be helpful to reduce the transmission in the community," says Elaine Shuo Feng, an infectious disease epidemiology researcher at the Oxford Vaccine Group at the University of Oxford.

Given the reality of asymptomatic spread, masks may be a good socially responsible insurance policy, Gottlieb argues. "[Wearing masks] protects other people from getting sick from you," he says.