Loneliness is a killer, more dangerous than obesity and smoking. Studies have found it leads to heart disease, stroke, and immune system problems, and it could even impair cancer recovery. A researcher at Copenhagen University Hospital in Denmark found loneliness a strong predictor of premature death, declining mental health, and lower quality of life in cardiovascular patients, and a Brigham Young University professor’s meta-analysis of studies from around the world found that socially isolated adults have a 50 percent greater risk of dying from any cause than people who have community.

That’s sobering, especially when you consider that 40 percent of American adults suffer from loneliness, according to an AARP study. And it’s one reason coliving—a new form of housing in which residents with similar interests, values, or intentions share living space, costs, and amenities—is exploding.

Coliving situations run a spectrum, from the resident-driven model to small homes with a half-dozen or so people to massive corporate complexes like The Collective tower with 550 beds in London. Residents, who stay anywhere from a few days to several years and usually don’t have to sign a lease or pay a security deposit, sleep in their own small private rooms (sometimes with bathrooms) and share common spaces such as large kitchens and dining areas, gardens, and work areas. They’re encouraged to interact with one another, often through organized happy hours and brunches. Ollie, which operates coliving spaces in New York and other cities, advertises that “friends are included.”

“Coliving is different than just having roommates, who may be people you found on Craigslist and just happen to share [your] living space. It’s done with more intention,” says Christine McDannell, who lived in unincorporated coliving houses for years before she launched Kindred Quarters, a coliving operator with homes in San Diego and Los Angeles, in 2017.

Author of The Coliving Code: How to Find Your Tribe, Share Resources, and Design Your Life, McDannell also runs Kndrd, a software company for coliving managers and residents, and she hosts the weekly Coliving Code Show every Wednesday on YouTube, iTunes, Soundcloud, and coliving.tv. She has watched—and helped—the industry grow up, and she’s amazed at how few, if any, horror stories she hears. That’s largely because millennials—by far the largest demographic among colivers—are accustomed to sharing and being held accountable through online reviews, she adds.

“You just don’t hear the crazy stories about roommating with strangers in an unfamiliar city,” she says. “When people write bad reviews, it’s usually about the Wi-Fi.”

As companies fat with funding expand into cities across the globe, coliving is newly corporatized—but it’s hardly a novel concept. Boarding houses provided rooms and shared meals for single men and women in the 19th and early 20th centuries; one of the most famous, the Barbizon Hotel in New York, was a “club residence for professional women” from 1927 until the 1980s.

People lived communally throughout most of history until industrialization facilitated privatization of family life and housing throughout the 20th century—with a few disruptions. In Israel, people have been living in communal villages called kibbutzim for more than 100 years. In the US, hippies attempted to create communes in the 1960s, but they were destroyed by free love, drugs, and egos (which did a lot to discourage coliving, even today).

At the same time in Denmark, however, cohousing (an earlier iteration of coliving) was emerging as a way to share childcare. Today, more than 700 communities thrive in Denmark. In Sweden, the government provides cohousing facilities.

A handful of cohousing communities following the Danish model have been established in the US, and hacker houses are common in tech capitals like Silicon Valley and Austin, Texas, but the concept has been slow to catch on until recently.

As it becomes increasingly impossible for mere mortals to afford skyrocketing rents in desirable cities, Americans are coming around to coliving and finding creative solutions to all sorts of social issues. Older women are shacking up together following the Golden Girls model. Coabode.org matches single moms who want to raise kids together. At Hope Meadows in Chicago, retirees live with foster kids.

The opportunity to pay lower rent (in many but not all cases) and share expenses makes all the difference in places like New York, San Francisco, Boston, and Los Angeles. When New York—based coliving operator Common opened a development with 24 furnished spaces in Los Angeles for between $1,300 and $1,800 a month, more than 9,000 people applied.

McDannell says coliving is exploding because it solves important challenges that plague modern society. “People are signing away their paychecks on rent and feeling increasingly isolated,” she wrote in “Why We’re Building a CoLiving Community Ecosystem” on LinkedIn. “It is due time that HaaS (Housing as a Service) disrupts the antiquated industry of property management and real estate.”