Should you wear a mask in public? The narrative is shifting.

One month ago, when just 57 people in the United States had tested positive for the coronavirus, the surgeon general tweeted in all caps: “STOP BUYING MASKS!”

Federal officials have stood by that guidance: Face masks are not effective in preventing the general public from getting the coronavirus, and there’s no reason for people who aren’t health-care workers or who don’t have the virus to wear them, especially as medical professionals face a mass shortage of protective equipment.

Now, roughly 175,000 Americans have tested positive for the coronavirus. And while experts still say people shouldn’t try to purchase medical-grade masks, the narrative on whether everyone should wear a homemade mask or facial covering when out in public is shifting.

Over the last several days, experts, officials, and some politicians have pushed the Centers for Disease Control and Prevention to revise its official guidance, pointing to other countries — including several nations in Asia, as well as the Czech Republic — that have either required masks or implemented mask-wearing campaigns and have seen some success in controlling the spread of the virus.

The CDC is now considering such a revision, one that would make clear people should not use medical-grade masks.

» READ MORE: CDC considers advising the public to wear face coverings

Among the officials pushing the CDC to update its guidance is Pennsylvania Sen. Pat Toomey, a Republican who released a video publicly supporting a social media campaign called #Masks4All, which encourages Americans to make homemade masks to wear when they must leave home for essentials. Toomey appears to be the only member of Congress to have so explicitly endorsed the campaign.

Over the weekend, Toomey pushed the issue in a call with Jay Butler, CDC deputy director for infectious diseases, according to Toomey spokesperson Steve Kelly. The CDC, he said, made no commitment to change its guidance. The CDC didn’t respond to a request for comment.

As of Tuesday, the CDC still recommends that sick people and caregivers wear masks, and notes that if masks aren’t available because they are reserved for health-care workers, a scarf or bandanna may have to suffice. While it doesn’t say that people without symptoms should not wear a mask or facial covering, it doesn’t say they should, either.

Kelly added that Toomey plans to speak with other public health officials in the coming days on what Kelly called “the commonsense nature of just having people cover their mouths and nose with a homemade mask or facial barrier when they absolutely must venture out of their homes.”

Other public officials have been less certain, including Pennsylvania Gov. Tom Wolf, who was asked Monday about Toomey’s video and said, “The jury is out [on] exactly what these masks do.” He said he would continue to review the science before making a recommendation one way or the other.

The #Masks4All campaign gained traction in the United States over the weekend after a San Francisco-based research scientist argued in the Washington Post that “we should all wear masks — store-bought or homemade — whenever we’re out in public.”

The researcher, Jeremy Howard, pointed to findings in dozens of scientific papers that indicate even the most basic of masks can be an effective tool in reducing virus transmission. A simple mask can be made without sewing by tying together two layers of a cut-up cotton blend T-shirt and covering the face and nose with it, being sure to wash the covering after each use.

There’s still plenty of disagreement among scientists and physicians, though. Some public health officials have warned that encouraging the large-scale wearing of masks will only further strain the health-care system’s limited resources and could embolden people to leave their homes for nonessential reasons.

Frequent hand-washing, avoiding touching your face, staying home as much as possible, and keeping at least six feet away from others remain the most effective ways to prevent the transmission of the virus, experts say.

“I think it’s really important that people might not become complacent [if] they have a homemade mask on,” Pennsylvania Health Secretary Rachel Levine said last week. "We want people to stay home.”

David Fleece, chief medical information officer at Temple University Hospital, told The Inquirer last week that, depending on the material, homemade masks "can approach the effectiveness of disposable surgical masks.” But, he warned, "if you are not using the right material and practicing really good hygiene, these efforts have the potential to make things worse by providing a false sense of security.”

Others have recommended a tailored approach. On Sunday, physician and former Food and Drug Commissioner Scott Gottlieb said on Face the Nation that the CDC should put out guidelines for how Americans can make a mask at home, and that encouraging mask-wearing in public can be a good “interim step” to transition some communities away from stay-at-home orders.

Flat surgical masks or DIY cotton masks aren’t necessarily to prevent the wearer from getting sick, he said, but about protecting others. The virus is transmitted through droplets of bodily fluids that can escape from the mouth and nose, so if someone who is infected is wearing a mask, “they’re much less likely to transmit infection.”

The CDC has for weeks recommended that sick people wear masks when they are around others or receiving medical care. But the virus can be spread by people who are not showing symptoms.

Judith J. Lightfoot, chief of infectious disease at Rowan University’s School of Osteopathic Medicine, is telling her patients to wear a mask or scarf over their mouth and nose while in public.

“We have seen this virus affect healthy people, so I can’t tell who has it and who does not have it,” she said last week. “I can’t say that you should not put on a mask. ... Everyone should do what they need to do to protect himself or herself.”

Neil Fishman, chief medical officer of the Hospital of the University of Pennsylvania, told the New York Times that wearing a mask makes sense for people who work in essential industries. He said masks can also keep people from touching their face, one of the main recommendations to preventing virus transmission, along with practicing good hand hygiene.

He said individuals can shed virus for about two days before they develop symptoms "and masking can prevent transmission from those individuals.”

Staff writer Justine McDaniel contributed to this article.