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 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, 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.