There’s a mandatory push for Americans to wear masks, but do they actually work? And are the government’s ever-changing policies on face masks reliable or helpful?

After weeks of obfuscation over the efficacy of face masks among federal agencies and controversy over health-care workers wearing disposable masks multiple times due to the lack of personal protective equipment, the Trump administration and New York Gov. Andrew Cuomo have agreed on one thing: all Americans should wear face masks in public settings when they’re not maintaining the recommended 6-feet distance from each other.

On Wednesday, Cuomo ordered all New Yorkers to cover their faces in public when they can’t maintain a proper social distance. “You’re walking down the street alone? Great! You’re now at an intersection and there are people at the intersection, and you’re going to be in proximity to other people? Put the mask on.” (On Thursday, he extended the lockdown until May 15.)

On April 3, the Trump administration and the Centers for Disease Control and Prevention also reversed their policies on face mask, and said all Americans should wear cloth face coverings and not — as it previously said — just medical workers. President Trump cited “recent studies” of asymptomatic transmission for the U-turn, while the CDC cited “new evidence.”

Unlike Cuomo’s executive order, the federal government’s recommendations are voluntary. Still, President Trump signaled his resistance to wearing a mask. “I don’t think I’m going to be doing it,” he said, adding, “Wearing a face mask as I greet presidents, prime ministers, dictators, kings, queens — I just don’t see it.”

“ Unlike Gov. Cuomo’s executive order, the federal government’s recommendations on face masks are voluntary. ”

Also Wednesday, New York Mayor Bill de Blasio called for all grocery stores in New York, the epicenter of the coronavirus pandemic in the U.S., to insist that customers wear masks while shopping. “I’m asking every store to put up a sign that you’re required to wear a face covering. This is another one of the things we have to do to protect each other,” he said at his daily press briefing.

“Everybody’s learning,” said Gregory Poland, who studies the immunogenetics of vaccine response in adults and children at the Mayo Clinic in Rochester, Minn. “We have just a few months experience with this virus. Face masks should be preserved for health-care workers who are at known obvious high risk.” And the DIY masks for everyone else? “They help as a memory aid not to touch your face.”

Coronavirus update: Worldwide, there were 2,402,798 million cases and 165,154 fatalities, as of Sunday evening. Nearly 243,000 of the 758,720 confirmed cases in the U.S. were in New York state. But New York City remains the national epicenter with at least 14,451 deaths, according to Johns Hopkins University’s Center for Systems Science and Engineering.

Timeline on the government’s changing position on masks

Jan 30: CDC says it doesn’t recommend the general public wear masks.

“The virus is not spreading in the general community,” Dr. Nancy Messonnier, director of the Center for the National Center for Immunization and Respiratory Diseases, said in a Jan. 30 briefing. “We don’t routinely recommend the use of face masks by the public to prevent respiratory illness. And we certainly are not recommending that at this time for this new virus.”

Feb 26: President Trump is asked what the U.S. doing to boost production of masks.

“Well, we can get a lot of it. In fact, we’ve ordered a lot of it just in case we need it. We may not need it; you understand that. But in case — we’re looking at worst-case scenario. We’re going to be set very quickly.”

Health and Human Services Secretary Alex Azar added: “These priorities are: First, expanding our surveillance network. Second, support for state and local governments’ work. Third and fourth, development of therapeutics and vaccines. And fifth, manufacturing and purchase of personal protective equipment like gowns and masks.”

Feb 29: Surgeon General tweets his opposition to the public wearing masks.

“Seriously people: STOP BUYING MASKS!” he tweeted. “They are NOT effective in preventing general public from catching #coronavirus, but if health-care providers can’t get them to care for sick patients, it puts them and our communities at risk!”

April 2: Mayor de Blasio says New York City’s residents should cover their face.

“It doesn’t have to be fancy to work. It can be real homegrown,” he said. “When you put on that face covering, you’re protecting everyone else. A lot of people out there, right this minute, don’t even know they have it.”

“You can create a face covering with anything you have at home right now, a piece of cloth,” he said. “You can create your own version and put on your own decoration. That’s what we want you to do. Something homemade, not something professional.”

“ On April 3, the CDC did a U-turn on its policy on face masks. The public was, understandably, confused. ”

April 3: New York Gov. Cuomo tells CNN that he’s skeptical improvised face masks work.

“Unless the fabric has a certain density, the virus will get through,” he said. “It couldn’t hurt unless it gives the person a false sense of security.”

April 3: The CDC does a U-turn and officially recommends masks at task force briefing.

It cites “new evidence” of community transmissions. “In light of this new evidence, CDC recommends 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 CDC said Americans should wear non-surgical cloth face masks to help prevent those with mild symptoms of COVID-19 or who are asymptomatic from spreading the virus. That recommendation was made so the wearer doesn’t pass on the virus. Prior to that, the CDC said that people should only wear face masks if they’re sick or caring for someone who is sick.

April 3: Trump says his administration recommends wearing cloth face coverings.

However, the president says he won’t wear a mask himself. “From recent studies, we know that the transmission from individuals without symptoms is playing a more significant role in the spread of the virus than previously understood,” Trump said adding, “You don’t have to do it. I’m choosing not to do it, but some people may want to do it and that’s OK. It may be good. Probably will.”

April 4: U.S. Surgeon General Jerome Adams posts 45-second do-it-yourself mask tutorial.

On Twitter TWTR, +2.03% he advises people use material and plastic bands rather than sewing: “Here’s how you can make your own face covering in a few easy steps with items you can find around the house, like an old scarf, a bandana or a hand towel, or you can make a face covering out of an old T-shirt.”

April 15: Cuomo issues executive order requiring New Yorkers to wear masks in public settings.

That includes a crosswalk, street corner, train or bus, supermarket and/or pharmacy, or anywhere where people are unable to maintain a 6-foot distance. “Put the mask on when you are not in socially distant places. It is your right to go out for a walk in the park, go out for a walk because you need to get out of the house. Fine, don’t infect me. You don’t have a right to infect me.”

The American public has been confused about whether face masks actually help. Getty Images

Will face masks help prevent transmission of coronavirus?

The public was, understandably, confused. N95 masks appear to be effective for health-care workers. This study says N95 medical-grade masks do help filter viruses that are larger than 0.1 micrometers (One micrometer, um, is one millionth of a meter.) The coronavirus is 0.125 um. They have “efficacy at filtering smaller particles and are designed to fit tightly to the face,” it said.

However, hospitals have reported a shortage of masks. Lawmakers say they should be used by medical staff who are up close and personal with patients who have COVID-19: Health and Human Services Secretary Alex Azar has said that there are only 30 million N95 masks in the national stockpile, and “as many as 300 million masks are needed in the U.S. for health-care workers.”

Dispatches from a pandemic:Letter from New York: ‘When I hear an ambulance, I wonder if there’s a coronavirus patient inside. Are there more 911 calls, or do I notice every distant siren?’

Others are even more skeptical than that. Paul Glasziou, a professor of medicine at Bond University in Australia, and Chris Del Mar, a professor of public health at Bond, analyzed a dozen studies on face masks. They concluded: “Face masks may not do much without eye protection.” Experts say masks may also remind people of the seriousness of this public-health emergency.

They say it’s best to avoid public settings. “People may also wear masks inappropriately, or touch a contaminated part of the mask when removing it and transfer the virus to their hand, then their eyes and thus to the nose,” they wrote in The Conversation. “Masks may also provide a false sense of security, meaning wearers might do riskier things such as going into crowded spaces and places.”

Want to make your own mask? Here’s a simple DIY approach.

Previous studies have concluded that face masks have helped reduce contagion by reducing droplets being sprayed into the air during flu season; another Japanese-based study says this works when paired with vaccination, not an option for most Americans. It may be that they work in a small amount of cases and/or just wearing them helps to promote healthy behaviors.

“ Masks may also provide a false sense of security. Wearers might do riskier things such as going into crowded spaces. ”

The scientists writing in The New England Journal of Medicine found that the novel coronavirus was detectable in the air for up to three hours, up to four hours on copper, up to 24 hours on cardboard, and up to two to three days on plastic and stainless steel. Above all else, health professionals recommend washing hands, cleaning surfaces and “social distancing” in public spaces.

Last week, New Jersey Gov. Philip Murphy, a Democrat, signed an order making it mandatory for all people over the age of 2 who are in grocery stores, pharmacies or any essential businesses in that state to wear some kind of cloth mask. “People talk about a new normal, I think that’s a reality,” he said, adding that social distancing may need to continue until 2022.

“ Last week, New Jersey’s governor signed an order making it mandatory for all people to wear masks in stores. ”

Labor unions have also been pushing for action. Kroger KR, +2.15% , the largest supermarket in the U.K., and the United Food and Commercial Workers International Union, America’s largest food and retail union, issued a joint statement Tuesday calling on federal and state government to designate associates at grocery stores as “extended first responders” or “emergency personnel.”

“Make no mistake, this designation is absolutely critical as it will ensure these frontline workers have priority access to personal protection equipment like masks and gloves,” Kroger Chairman and Chief Executive Rodney McMullen and UFCW International President Marc Perrone said in a joint statement. Such a designation would give these workers priority for coronavirus testing.

McMullen and Perrone said that their supermarket workers “have been working tirelessly to make sure that millions of American families have the fresh food and products they need. As all Americans are now witnessing — grocery workers play a critical role in our communities and they must be protected.” They added, “We urge our national and statewide elected leaders to act now.”

(Elisabeth Buchwald contributed to this story.)