Should healthy people be wearing masks when they’re outside to protect themselves and others?

Both the World Health Organization and the Centers for Disease Control and Prevention have repeatedly said that ordinary citizens do not need to wear masks unless they are sick and coughing. And as health care workers around the world face shortages of N95 masks and protective gear, public health officials have warned people not to hoard masks.

But those official guidelines may be shifting.

On Monday during the coronavirus task force briefing, President Donald Trump was asked whether Americans should wear nonmedical masks. “That’s certainly something we could discuss,” he said. “It could be something like that for a limited period of time.”

Dr. Robert Redfield, director of the CDC, confirmed in an interview with National Public Radio on Monday that the agency was reviewing its guidelines on who should wear masks. Citing new data that shows high rates of transmission from people who are infected but show no symptoms, he said the guidance on mask wearing was “being critically re-reviewed, to see if there’s potential additional value for individuals that are infected or individuals that may be asymptomatically infected.”

The coronavirus is probably three times as infectious as the flu, Redfield said. The proportion of people who are infected but asymptomatic — for 48 hours or so before showing any signs of fever, cough or other signs of the disease — may be as high as 25%, he said.

“That’s important, because now you have individuals that may not have any symptoms that can contribute to transmission, and we have learned that in fact they do contribute to transmission,” Redfield said.

A federal official said Tuesday that the CDC’s review of mask wearing for the public stemmed from a request by the White House coronavirus task force, which is leaning toward recommending it.

One concern, which Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, voiced on CNN, is that such a recommendation could cause even worse shortages of N95 and other medical masks for health care workers, who need them most.

“You don’t want to take masks away from the health care providers who are in a real and present danger of getting infected,” Fauci, a member of the task force, said on CNN on Tuesday morning.

Nonetheless, Fauci said: “The idea of getting a much more broad communitywide use of masks outside of the health care setting is under very active discussion at the task force. The CDC group is looking at that very carefully.”

Masks work by stopping infected droplets spewing from the wearer’s nose or mouth, rather than stopping the acquisition of the virus from others. Both medical-grade N95 masks and flat face masks are made of a special melt-blown fabric, which is able to stop infectious particles even finer than a micron in diameter. But in many Asian countries, where everyone is encouraged to wear masks, the approach is about crowd psychology and protection.

If everyone wears a mask, individuals protect one another, reducing overall community transmission.