At the urging of national health officials, Minnesotans now are being asked to wear cloth face masks when they head out to grocery stores and other public places.

Friday's recommendation from the CDC, an effort to slow the spread of COVID-19, came with a strong plea that the public preserve medical-grade masks for health care providers, as well as a warning that masks are no substitute for social distancing and thorough, frequent hand-washing.

When the pandemic first hit the United States, the CDC said only people who were infected or showed symptoms should wear a mask in public. But as infections and deaths across the country multiplied, the CDC began reconsidering its advice.

Before the new recommendation was announced, Minnesota health experts had expressed caution about the value of wearing cloth masks in public. In short, they said, there are little data to assess the value of the homemade masks. And yet they agree that masks could keep people who are infected but have no symptoms from spreading the virus through coughs, sneezes or even talking.

If the CDC recommends it, that's what people should do, said Helen Strike, who oversees Allina Health's COVID-19 response team and is president of two of its hospitals.

"At this point, we have to do everything we can to flatten this curve," she said. "At some point, we're going to look back on this and we're going to figure out what's the best practice. Right now, we're trying everything we can."

The push for the public to wear makeshift masks comes as cities and states strain to get necessary medical supplies for health care providers exposed to infected people. At one point, the CDC recommended that health care providers use homemade masks, saying even a bandanna or scarf would do if no medical-grade masks were available.

"Oh, my God," said Deb Dittberner, a family physician in Alexandria, Minn. "We need something better than bandannas."

So she and legions of Minnesotans who sew have churned out thousands of masks for medical care providers. Their overwhelming response quickly emptied store shelves of elastic, interfacing and twill tape.

To be clear, using cloth masks in hospitals and clinics remains a stop-gap measure until manufacturers can ramp up production of high-grade medical masks. "When we have nothing else, we'll be using it," Dittberner said.

Allina health care facilities are laundering piles of donated cloth masks and using them in clinics for patients with respiratory symptoms.

Eventually, they may be used by Allina staff who don't deal directly with patients.

Lakeville's Julie Skovran and her 19 "sewing angels" have stitched more than 500 masks, sending them to Presbyterian Homes in Bloomington as well as to care providers in hospices and a hospital pediatric unit.

There's an even larger workforce that could use the cloth masks, including day-care providers, EMS workers, police officers, firefighters and assisted living facilities' administrative staffs and cleaning crews, Dittberner said.

What's more, the cloth mask may become the public's best defense against the infection, she said.

In some Asian countries, wearing a face mask in public is the norm during an epidemic. In the Czech Republic, officials recently mandated that face masks be worn in public, citing the idea that, "My mask protects you. Your mask protects me."

The theory promoting universal mask-wearing is that it could keep people who are ill from sharing the virus, said Dr. Susan Kline, a professor in the division of infectious diseases and international medicine at the University of Minnesota.

The effectiveness of the N95 mask, which fits tightly on the face and is made of material that allows for a high level of filtration, is proven, she said. "They're carefully engineered and tested," Kline said.

"The world demand for these supplies had skyrocketed," Kline said. "We can't even meet the need for our health care facilities."

For the general public, cloth masks, although unregulated and untested but now recommended by the CDC, may have to be good enough, she said.

The key is to make sure the mask fits tightly, covers the lower part of the nose and entire mouth, and tucks under the chin and is securely fastened.

There should be no gaps, Kline said.

As the pandemic has swept the United States, a multitude of designs and free patterns for DIY face masks have popped up on the internet.

Michele Hoaglund, owner of Treadle Yard Goods in St. Paul, has partnered with the nonprofit Sew Good Goods, Allina and Blue Cross Blue Shield to churn out masks for health care workers from designs approved by Allina. Her shop, open only for curbside pickup, provides free kits to volunteers and includes tightly woven fabric for the outside of the mask, 100% cotton flannel for the inside and elastic — if she has it in stock.

"People are doing this because it's something they can do," Hoaglund said.

That idea inspired Shannon Williamson, who has a University of Minnesota degree in apparel design and medical device innovation, to come up with her own design after consulting with experts, including engineers, physicians and material scientists.

The design includes a pocket to accommodate a filter — even something as simple as a vacuum bag or coffee filter.

"The reason the N95 mask is so wonderful is because it's a tight fit," Williamson said. Her design allows for a tighter fit than many simpler designs.

"There's nothing wrong with many of those," she said. "The best mask is one that's worn."

Staff writer Christopher Snowbeck and the New York Times contributed to this report.