Widespread use of nonmedical masks could reduce community transmission.

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

Dr. Robert Redfield, the director of the C.D.C., confirmed in an interview with WABE in Atlanta, a National Public Radio member station, 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, Dr. Redfield said. Some people are infected and transmitting the virus probably as long as two days before showing any symptoms, he said. “This helps explain how rapidly this virus continues to spread across the country, because we have asymptomatic transmitters and we have individuals who are transmitting 48 hours before they become symptomatic,” Dr. Redfield said in the interview.

“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,” Dr. Redfield said.

A federal official said Tuesday that the C.D.C.’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.

Nonetheless, Dr. Fauci said: “The idea of broad communitywide use of masks outside of the health care setting is under very active discussion at the task force. The C.D.C. 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 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. And places like Hong Kong and Taiwan that jumped to action early with social distancing and universal mask wearing have gotten their cases under much greater control.

There have been troubling reports that indicate the coronavirus may be able to travel farther in the air and stay in the environment longer than is possible by respiratory droplets, which have so far been assumed to be the primary mode of transmission of the virus.

One study in Singapore found traces of the virus in air vents in patient isolation rooms. In another study, researchers at the University of Nebraska Medical Center detected extensive contamination in patient rooms as well as in air samples collected from the hallways outside rooms.

Dr. Scott Gottlieb, the former commissioner of the Food and Drug Administration, said in an interview on Sunday that the C.D.C. should put out designs for cloth masks for the public. “The value of the mask isn’t necessarily to protect you from getting sick, although it may offer some protection,” he told CBS news. “It’s to protect you from other people. So when someone who’s infected is wearing a mask, they’re much less likely to transmit infection.”

He said studies involving the flu suggested that you could reduce your ability to spread the flu by about 50 percent if you wore a mask.

This is what the C.D.C.’s guidelines currently say:

“If you are sick: You should wear a face mask, if available, when you are around other people (including before you enter a health care provider’s office). If you are caring for others: If the person who is sick is not able to wear a face mask (for example, because it causes trouble breathing), then as their caregiver, you should wear a face mask when in the same room with them. Visitors, other than caregivers, are not recommended.

“Note: During a public health emergency, face masks may be reserved for health care workers. You may need to improvise a face mask using a scarf or bandana.”

In the radio interview, Dr. Redfield also emphasized that social distancing, staying at least six feet away from others in public spaces, and staying home, were important measures to keep in place for now.