With medical supplies urgently needed by health care workers, Stephanie Cave of Dorchester was moved to help by an impulse both altruistic and creative. She sat down at her sewing machine and began to stitch together cloth face masks. Then she realized she knew a lot of other people who might want to do the same thing.

“I teach sewing classes over at the Dorchester Stitch House and I have a lot of sewing friends all over the place,” she said. “So I just reached out to those groups and there were other people eager to share and do something.”

In less than a week, a Facebook group she started ballooned to more than 500 members. Her group is one of many devoted to making masks here in Massachusetts and across the country.

Cave, who cares for her toddler during the day, spends the rest of her waking hours running an all-volunteer operation that, in the last week, has delivered 2,000 face masks to homeless shelters, assisted living facilities and hospitals. And while health care providers have come to depend on cloth masks while facing an international shortage of disposable surgical masks, the little research that's been done to compare the two has proven that cloth masks are nowhere near as effective as the industry standard.

While homemade masks are new to hospitals in the U.S., they’ve long been used by health care workers around the world. One of the few studies examining their effectiveness compared the use of cloth masks and disposable surgical ones at 14 hospitals in Vietnam. The findings,published in the "British Medical Journal" in 2015, indicated respiratory and viral particles penetrated 97 percent of cloth masks compared to 44 percent of disposable surgical masks.

The Cambridge Health Alliance, which operates community hospitals in Cambridge, Somerville and Everett, is one of the recipients of cloth masks made by Cave's group. Like many other groups, they are about to start feeling the strain of the mask shortage.

“Right now, we have more than three weeks of supplies of pretty much everything we need,” said Jill Batty, chief financial officer of the Cambridge Health Alliance. “But this is going to last longer than three weeks. And right now, the supply chain is extremely challenged.”

Batty said her organization is relying on volunteers to supply as many as 500 homemade masks each week.

“We looked at our supply room assets and said, ‘Well, OK, those aren’t going to be enough,’” she said. “And then we looked at our other assets, and our other assets were our community support and innovation.”

The 2015 study of mask use in Vietnam has popped up in a lot of internet searches lately, and its author,

Raina MacIntyre, a biosecurity researcher at the University of New South Wales in Australia, said she’s been fielding inquiries from health care workers asking the same question: Is it better for me not to wear a mask? Her answer is an emphatic no. Even a cloth mask, she said, is better than nothing at all.

“Probably some physical barrier across your nose and mouth will help because it will stop you from self-contaminating with your hand,” MacIntyre said.

But she stressed that homemade cloth masks don’t meet the standard for personal protective equipment (PPE) — something she saidfrontline health care workers must have.

“You should not be working without any PPE or inadequate PPE. It’s a work, health and safety matter,” MacIntyre said. “There’s no point in our health care workers also getting infected or dying.”

Cambridge Health Alliance is doing two things with their cloth masks that, MacIntyre said, make a lot of sense.

First, they’re giving them to people not involved in direct patient care — including food, cleaning and reception staff. And second, the hospital chain worked with an infectious disease doctor to design a pocket for a filter.

MacIntyre said filters are available online and vastly improve the ability of even cloth masks to protect against particles. Still, she said, resourcefulness is not enough.

“There’s going to be a lot of reflection that needs to happen and maybe even formal inquiries about the way wealthy countries have dealt with this pandemic,” MacIntyre predicted. “Why didn’t we have adequate stockpiles for our health workers? Why do we treat health workers like disposable assets?”

Health care workers — and everyone else — are of course on the minds of people like Stephanie Cave, ramping up production in what’s become a cottage industry of face mask making. She’s working to fill requests for at least 2,000 more.

“I’m really happy,” she said. “I can sew fast.”