CHICAGO >> For weeks, officials from the White House to Chicago’s City Hall told people that wearing a face mask in public isn’t necessary as the novel coronavirus spread — and that it could even cause more harm than good.

But other countries took a different route, especially some Asian nations — including South Korea, Hong Kong and Singapore — where mask wearing became common practice. In Europe, the Czech Republic went so far as to require that people wear masks when they venture from their homes. Public health officials in those nations contend that widespread mask use limited the scope of their outbreaks, or “flattened the curve” in pandemic parlance.

Medical professionals are taking notice, and some are now pressing for more frequent mask wearing. Writing in the British medical journal The Lancet, a group of scientists suggested “universal use of face masks could be considered if supplies permit.”

The supply question is key, especially amid a grave shortage of the masks used by front-line medical workers in the United States. Advocates say they aren’t encouraging people to buy specialized N95 respirator masks or even regular surgical masks. Clean, homemade cloth masks that cover the nose and mouth will do the trick, they say.

“I think if everyone used masks, it would decrease the amount of transmission of the virus,” said Dr. Rahul Khare, CEO of the Innovative Express Care immediate care facility in Chicago. “By putting a face mask over your nose and mouth, you’re decreasing the amount of the virus particles and therefore decreasing transmission rates.”

Khare said he wants government officials to switch gears and advise people to wear masks if they must leave their homes. The federal Centers for Disease Control and Prevention is reportedly considering new guidance on the subject, while President Donald Trump has said it might not be a bad idea.

But the science is not definitive, and opinions on the president’s coronavirus task force, which works with the CDC to make recommendations, are not unanimous.

Surgeon General Jerome Adams this week was still expressing deep reservations during an appearance on television’s “Fox & Friends.” And even those who advocate for wearing masks don’t want people to feel like they can ignore stay-at-home orders if they use a mask.

Nevertheless, medical opinions and government advice appear to be shifting.

After discouraging people early in the pandemic from hoarding masks that are in short supply and badly needed by medical personnel, Gov J.B. Pritzker on Wednesday said “we’re thinking about” advising people to wear masks.

“I would not discourage people from wearing masks, and in fact I think that there’s some evidence to show it can be effective,” Pritzker said.

Dr. Allison Arwady, director of the Chicago Public Health Department, also began to soften her earlier stance that masks won’t help much and could even cause people to touch their face more frequently — a big no-no given the highly contagious nature of the virus.

Arwady said new studies have concluded that some people who are infected with the new coronavirus have no symptoms. But they can still spread the virus, making others sick, and wearing a mask could reduce that risk, she said.

“We’ll continue to make changes to our recommendations if we think that’s necessary,” she said Wednesday. “Stay tuned.”

She made her comments at a news conference called by Mayor Lori Lightfoot, who quickly stepped up to the microphone to make sure people understand that even if the advice changes, people must still try to stay at home, wash their hands frequently and absolutely not leave the house if they are feeling sick.

“I don’t want people to think that the mask makes them invincible, because it doesn’t,” Lightfoot said. “I don’t want people to be misled that simply because you wear a mask you are fine going out and not practicing any of the other guidance that goes along with that.”

Asked why the advice is shifting, Khare and other experts said authorities were initially afraid of people buying up medical-grade masks. They also were worried about sowing fear, he said.

Potential hoarding of the high-quality masks — such as the N95 respirator masks the world is learning so much about these days — is indeed a concern, said Dr. Robert Murphy, executive director of the Institute for Global Health at the Northwestern University Feinberg School of Medicine. “The hospitals can’t even get the damn masks,” he said, calling the shortage “a national disgrace and embarrassment.”

Khare said he’s not suggesting that people go out and buy medical-quality masks, but rather that they should fashion their own. While not as protective as the masks used in hospitals and clinics, homemade fabric versions could still reduce the spread of the virus. “Bandanas, cloths, anything you put over your nose and your mouth,” Khare said.

As the idea of wearing a mask spreads, many businesses and groups have begun posting tutorials on how to make masks at home. Some groups have begun coordinating efforts to sew homemade masks.

The idea of wearing a mask, Murphy said, is not to protect oneself but to protect others.

“Originally, we were not recommending that because it does not protect the person wearing the mask from getting infected,” Murphy said. “What the mask does is protect the people around you in case you are infected and don’t know it.”

“People will think, ‘I have the mask, I’m not going to get it,’ ” Murphy added. “That’s not why you wear the mask. You wear the mask because you might have it and give it to somebody else.”

And the days of trying to avoid frightening the populace are over, Khare said.

“We’re here and we know what this virus is doing now,” said Khare, adding that he believes wearing a mask also provides some protection from getting infected. “And looking at the science, I think it’s clear that the risks of wearing masks is very low, and the benefits of wearing masks is very high.”