Los Angeles Mayor Eric Garcetti (D) on Wednesday called on the city’s millions of residents to start covering their faces whenever they are out in public as part of an effort to combat the outbreak of the novel coronavirus. 

Garcetti said on Twitter that the decision was guided by data showing that many of those infected with the virus are asymptomatic. 

“[It is] why we are recommending you use cloth face coverings plus physical distancing for essential activities,” he said, advising against using “surgical and N95 masks, which are reserved for first responders and medical workers.”

Early data suggests many who are infected are not symptomatic, which is why we are recommending you use cloth face coverings plus physical distancing for essential activities.

Do not use surgical and N95 masks, which are reserved for first responders and medical workers.

— MayorOfLA (@MayorOfLA) April 1, 2020

The mayor noted in a press conference that night that he had been waiting for guidance from the Centers for Disease Control and Prevention (CDC) on whether to issue the advisory. But he said that he elected to make the move without CDC communication after seeing the number of confirmed virus cases continue to climb in the region. 

“To be clear, you should still stay at home. This isn’t an excuse to suddenly all go out,” Garcetti said.

He reported that 3,518 cases of COVID-19 had been confirmed in Los Angeles County as of Wednesday evening, an 18 percent increase from the previous day. Cases in Los Angeles County have doubled since last Friday, Garcetti noted. 

Garcetti’s announcement was coupled with a new advisory from the California Department of Public Health on the use of cloth face coverings. The department said it would not require individuals to wear the coverings if they go out in public, however. 

“Face coverings are not a substitute for physical distancing or frequent hand washing, which we know are amongst the most effective ways to reduce the spread of COVID-19,” Dr. Sonia Angell, director of the California Department of Public Health and state health officer, said in a statement. 

California Gov. Gavin Newsom (D) echoed Angell’s comments, saying in a news conference that the new guidance in Los Angeles was not a “substitute for a stay-at-home order.” 

Questions over the necessity of face masks have mounted in recent weeks, especially as hospitals struggle with obtaining necessary equipment for workers dealing with a surge in patients. U.S. and global health officials have said that people should not wear masks in public unless they are sick. 

Though Anthony Fauci, a physician and the government’s top infectious disease expert, said earlier this week that the administration was seriously considering putting in place guidelines for citizens to wear protective coverings over their face. 

Angell said that the face coverings could “help reduce the spread of infectious particles from those who could be infected but don’t have symptoms.” She also noted that the garment could help emphasize social-distancing measures in public.