The Centers for Disease Control and Prevention called for all Americans to wear face coverings in public to help stop the spread of the coronavirus Friday, pushing for people to wear cloth coverings like a bandana or a scarf.

Announcing the move at his daily briefing, President Trump undermined the recommendation of his experts by emphasizing that it was voluntary and he would not be wearing one.

“So it’s voluntary, you don’t have to do it,” he said. “They suggest it for a period of time. This is voluntary, I don’t think I’m gonna be doing it.”

In the recommendation published online Friday, the CDC said that because the virus can “spread between people interacting in close proximity,” they would recommend “wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially in areas of significant community-based transmission.”

The recommendation is less about preventing the wearer from contracting the coronavirus themselves than it is about limiting asymptomatic people from unknowingly spreading the disease. Wearing cloth masks, the CDC said, could “help people who may have the virus and do not know it from transmitting it to others.”

Trump, asked about his stance on masks later in Friday's press briefing, said, “I just don't want to wear one myself. It's a recommendation, they recommend it. I'm feeling good. I just don't want to be doing, I don't know, somehow, sitting in the Oval Office behind that beautiful Resolute Desk, the great Resolute Desk, I think wearing a face mask as I greet presidents, prime ministers, dictators, kings, queens, I don't know, I don't see it for myself."

The Washington Post first reported Thursday that the White House would soon issue the guidance. The call represents a shift from earlier recommendations from the White House and comes in response to studies that found people without symptoms can still spread the virus.

BuzzFeed News reported earlier this week on concerns about the availability of face masks and questions about how effective homemade or fabric masks are in stopping the spread of the virus. Previously, the CDC has said that people do not need to wear masks unless they are coughing or sneezing, in part to preserve a short supply of masks for health care workers. But public heath officials told BuzzFeed News that the CDC’s guidance, while appropriate at the time, should evolve to encourage the use of masks.

Trump and the CDC said Friday that the recommendation was not calling for people to wear surgical masks or N95 respirators, saying those should be reserved for health care workers on the front lines.

In recent days, Los Angeles County and New York state have encouraged residents to wear face coverings in public places to help stop the spread of the virus, but officials warned that masks should not give people a false sense of security.

“Face coverings could provide some additional protection against COVID-19, but Californians should not have a false sense of security if they choose to wear them. Make sure you’re also staying 6 feet away from other people if you have to leave your home to get groceries or prescriptions,” California Health and Human Services Secretary Dr. Mark Ghaly said in a statement Thursday.

But there is not much information on how much protection fabric or other homemade face masks can offer. While they may block larger droplets of water, they don’t protect against smaller particles in the air. One small study from 2013 suggested fabric masks are three times less effective than surgical masks.

As Roger Shapiro, a Boston doctor and an associate professor of immunology and infectious diseases at Harvard, told BuzzFeed News this week, “The first reason to wear a mask is so we all protect each other,” and so that “you don’t infect someone else.”