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We’re getting lonelier.

The General Social Survey found that the number of Americans with no close friends has tripled since 1985. “Zero” is the most common number of confidants, reported by almost a quarter of those surveyed. Likewise, the average number of people Americans feel they can talk to about "important matters" has fallen from three to two.

Mysteriously, appears most prevalent among millennials. I see two compounding explanations.

First, incredibly, loneliness is contagious. A 2009 study using data collected from roughly 5,000 people and their offspring from Framingham, Massachusetts, since 1948 found that participants are 52 percent more likely to be lonely if someone they’re directly connected to (such as a friend, neighbor, co-worker, or family member) is lonely. People who aren’t lonely tend to then become lonelier if they’re around people who are.

Why? Lonely people are less able to pick up on positive social stimuli, like others’ and commitment signals, so they withdraw prematurely – in many cases before they’re actually socially isolated. Their inexplicable withdrawal may, in turn, make their close connections feel lonely too. Lonely people also tend to act “in a less trusting and more hostile fashion,” which may further sever social ties and impart loneliness to others.

This is how, as Dr. Nicholas Christakis told the New York Times in a 2009 article on the Framingham findings, one lonely person can “destabilize an entire ,” like a single thread unraveling a sweater:

"If you’re lonely, you transmit loneliness, and then you cut the tie or the other person cuts the tie. But now that person has been affected, and they proceed to behave the same way. There is this cascade of loneliness that causes a disintegration of the social network."

Like other contagions, loneliness is bad for you. Lonely adolescents exhibit more social stress compared to not lonely ones. Individuals who feel lonely also have significantly higher Epstein-Barr virus antibodies (the key player in mononucleosis). Lonely women literally feel hungrier. Finally, feeling lonely increases risk of death by 26 percent and doubles our risk of dying from heart disease.

But if loneliness is inherently contagious, why has it just recently gotten worse?

The second reason for millennial loneliness is the Internet makes it viral. It’s not a coincidence that loneliness began to surge two years after Apple launched its first commercial personal computer and five years before Tim Berners-Lee invented the World Wide Web.

Ironically, we use the Internet to alleviate our loneliness. Social connection no longer requires a car, phone call, or plan – just a click. And it seems to work: World of Warcraft players experience less and less loneliness when online than in the real world. The Internet temporarily enhances the social satisfaction and behavior of lonely people, who are more likely to go online when they feel isolated, , or .

The Internet provides, as David Brooks wrote in a New York Times column last fall, “a day of happy touch points.”

But the Internet can eventually isolate us and stunt our remaining relationships. Since Robert Putnam’s famous 2000 book Bowling Alone, the breakdown of community and civic society has almost certainly gotten worse. Today, going to a bowling alley alone, Putnam’s central symbol of “social capital deficit,” would actually be definitively social. Instead, we’re “bowling” – and a host of other pseudo-social acts – online.

One reason the Internet makes us lonely is we attempt to substitute real relationships with online relationships. Though we temporarily feel better when we engage others virtually, these connections tend to be superficial and ultimately dissatisfying. Online social contacts are “not an effective alternative for offline social interactions,” sums one study.

In fact, the very presence of technology can hinder genuine offline connection. Simply having a phone nearby caused pairs of strangers to rate their conversation as less meaningful, their conversation partners as less , and their new relationship as less close than strangers with a notebook nearby instead.

Excessive Internet use also increases feelings of loneliness because it disconnects us from the real world. Research shows that lonely people use the Internet to “feel totally absorbed online” – a state that inevitably subtracts time and energy that could otherwise be spent on social activities and building more fulfilling offline friendships.

Further exacerbating our isolation is society’s tendency to ostracize lonely peers. One famous 1965 study found that when monkeys were confined to a solitary isolation chamber called the “pit of despair” and reintroduced to their colony months later, they were shunned and excluded. The Framingham study suggested that humans may also drive away the lonely, so that “feeling socially isolated can lead to one becoming objectively isolated.”

The more isolated we feel, the more we retreat online, forging a virtual escape from loneliness. This is particularly true for my generation, who learned to self-soothe with technology from a young age. It will only become more true as we flock to freelancing and other means of working alone.

In his controversial 1970 book The Pursuit of Loneliness, sociologist Phillip Slater coined the “Toilet Assumption”: our belief that undesirable feelings and social realities will “simply disappear if we ignore them.” Slater argued that America’s individualism and, in turn, our loneliness “is rooted in the attempt to deny the reality of human interdependence.” The Internet is perhaps the best example to date of our futile attempt to flush away loneliness.

Instead, we’re stuck with a mounting pile of infectious isolation.

A version of this article originally appeared on Forbes. Sign up for my newsletter to get my articles delivered straight to your inbox.