More comfortable online than out partying, post-Millennials are safer, physically, than adolescents have ever been. But they’re on the brink of a mental-health crisis.

one day last summer, around noon, I called Athena, a 13-year-old who lives in Houston, Texas. She answered her phone—she’s had an iPhone since she was 11—sounding as if she’d just woken up. We chatted about her favorite songs and TV shows, and I asked her what she likes to do with her friends. “We go to the mall,” she said. “Do your parents drop you off?,” I asked, recalling my own middle-school days, in the 1980s, when I’d enjoy a few parent-free hours shopping with my friends. “No—I go with my family,” she replied. “We’ll go with my mom and brothers and walk a little behind them. I just have to tell my mom where we’re going. I have to check in every hour or every 30 minutes.”

Those mall trips are infrequent—about once a month. More often, Athena and her friends spend time together on their phones, unchaperoned. Unlike the teens of my generation, who might have spent an evening tying up the family landline with gossip, they talk on Snapchat, the smartphone app that allows users to send pictures and videos that quickly disappear. They make sure to keep up their Snapstreaks, which show how many days in a row they have Snapchatted with each other. Sometimes they save screenshots of particularly ridiculous pictures of friends. “It’s good blackmail,” Athena said. (Because she’s a minor, I’m not using her real name.) She told me she’d spent most of the summer hanging out alone in her room with her phone. That’s just the way her generation is, she said. “We didn’t have a choice to know any life without iPads or iPhones. I think we like our phones more than we like actual people.”

I’ve been researching generational differences for 25 years, starting when I was a 22-year-old doctoral student in psychology. Typically, the characteristics that come to define a generation appear gradually, and along a continuum. Beliefs and behaviors that were already rising simply continue to do so. Millennials, for instance, are a highly individualistic generation, but individualism had been increasing since the Baby Boomers turned on, tuned in, and dropped out. I had grown accustomed to line graphs of trends that looked like modest hills and valleys. Then I began studying Athena’s generation.

Around 2012, I noticed abrupt shifts in teen behaviors and emotional states. The gentle slopes of the line graphs became steep mountains and sheer cliffs, and many of the distinctive characteristics of the Millennial generation began to disappear. In all my analyses of generational data—some reaching back to the 1930s—I had never seen anything like it.

The allure of independence, so powerful to previous generations, holds less sway over today’s teens.

At first I presumed these might be blips, but the trends persisted, across several years and a series of national surveys. The changes weren’t just in degree, but in kind. The biggest difference between the Millennials and their predecessors was in how they viewed the world; teens today differ from the Millennials not just in their views but in how they spend their time. The experiences they have every day are radically different from those of the generation that came of age just a few years before them.

What happened in 2012 to cause such dramatic shifts in behavior? It was after the Great Recession, which officially lasted from 2007 to 2009 and had a starker effect on Millennials trying to find a place in a sputtering economy. But it was exactly the moment when the proportion of Americans who owned a smartphone surpassed 50 percent.

The more I pored over yearly surveys of teen attitudes and behaviors, and the more I talked with young people like Athena, the clearer it became that theirs is a generation shaped by the smartphone and by the concomitant rise of social media. I call them iGen. Born between 1995 and 2012, members of this generation are growing up with smartphones, have an Instagram account before they start high school, and do not remember a time before the internet. The Millennials grew up with the web as well, but it wasn’t ever-present in their lives, at hand at all times, day and night. iGen’s oldest members were early adolescents when the iPhone was introduced, in 2007, and high-school students when the iPad entered the scene, in 2010. A 2017 survey of more than 5,000 American teens found that three out of four owned an iPhone.

The advent of the smartphone and its cousin the tablet was followed quickly by hand-wringing about the deleterious effects of “screen time.” But the impact of these devices has not been fully appreciated, and goes far beyond the usual concerns about curtailed attention spans. The arrival of the smartphone has radically changed every aspect of teenagers’ lives, from the nature of their social interactions to their mental health. These changes have affected young people in every corner of the nation and in every type of household. The trends appear among teens poor and rich; of every ethnic background; in cities, suburbs, and small towns. Where there are cell towers, there are teens living their lives on their smartphone.

To those of us who fondly recall a more analog adolescence, this may seem foreign and troubling. The aim of generational study, however, is not to succumb to nostalgia for the way things used to be; it’s to understand how they are now. Some generational changes are positive, some are negative, and many are both. More comfortable in their bedrooms than in a car or at a party, today’s teens are physically safer than teens have ever been. They’re markedly less likely to get into a car accident and, having less of a taste for alcohol than their predecessors, are less susceptible to drinking’s attendant ills.

Psychologically, however, they are more vulnerable than Millennials were: Rates of teen depression and suicide have skyrocketed since 2011. It’s not an exaggeration to describe iGen as being on the brink of the worst mental-health crisis in decades. Much of this deterioration can be traced to their phones.

Even when a seismic event—a war, a technological leap, a free concert in the mud—plays an outsize role in shaping a group of young people, no single factor ever defines a generation. Parenting styles continue to change, as do school curricula and culture, and these things matter. But the twin rise of the smartphone and social media has caused an earthquake of a magnitude we’ve not seen in a very long time, if ever. There is compelling evidence that the devices we’ve placed in young people’s hands are having profound effects on their lives—and making them seriously unhappy.

In the early 1970s, the photographer Bill Yates shot a series of portraits at the Sweetheart Roller Skating Rink in Tampa, Florida. In one, a shirtless teen stands with a large bottle of peppermint schnapps stuck in the waistband of his jeans. In another, a boy who looks no older than 12 poses with a cigarette in his mouth. The rink was a place where kids could get away from their parents and inhabit a world of their own, a world where they could drink, smoke, and make out in the backs of their cars. In stark black-and-white, the adolescent Boomers gaze at Yates’s camera with the self-confidence born of making your own choices—even if, perhaps especially if, your parents wouldn’t think they were the right ones.

Fifteen years later, during my own teenage years as a member of Generation X, smoking had lost some of its romance, but independence was definitely still in. My friends and I plotted to get our driver’s license as soon as we could, making DMV appointments for the day we turned 16 and using our newfound freedom to escape the confines of our suburban neighborhood. Asked by our parents, “When will you be home?,” we replied, “When do I have to be?”

Today’s teens are also less likely to date. The initial stage of courtship, which Gen Xers called “liking” (as in “Ooh, he likes you!”), kids now call “talking”—an ironic choice for a generation that prefers texting to actual conversation. After two teens have “talked” for a while, they might start dating. But only about 56 percent of high-school seniors in 2015 went out on dates; for Boomers and Gen Xers, the number was about 85 percent.

The decline in dating tracks with a decline in sexual activity. The drop is the sharpest for ninth-graders, among whom the number of sexually active teens has been cut by almost 40 percent since 1991. The average teen now has had sex for the first time by the spring of 11th grade, a full year later than the average Gen Xer. Fewer teens having sex has contributed to what many see as one of the most positive youth trends in recent years: The teen birth rate hit an all-time low in 2016, down 67 percent since its modern peak, in 1991.

Independence isn’t free—you need some money in your pocket to pay for gas, or for that bottle of schnapps. In earlier eras, kids worked in great numbers, eager to finance their freedom or prodded by their parents to learn the value of a dollar. But iGen teens aren’t working (or managing their own money) as much. In the late 1970s, 77 percent of high-school seniors worked for pay during the school year; by the mid-2010s, only 55 percent did. The number of eighth-graders who work for pay has been cut in half. These declines accelerated during the Great Recession, but teen employment has not bounced back, even though job availability has.

Of course, putting off the responsibilities of adulthood is not an iGen innovation. Gen Xers, in the 1990s, were the first to postpone the traditional markers of adulthood. Young Gen Xers were just about as likely to drive, drink alcohol, and date as young Boomers had been, and more likely to have sex and get pregnant as teens. But as they left their teenage years behind, Gen Xers married and started careers later than their Boomer predecessors had.

Why are today’s teens waiting longer to take on both the responsibilities and the pleasures of adulthood? Shifts in the economy, and parenting, certainly play a role. In an information economy that rewards higher education more than early work history, parents may be inclined to encourage their kids to stay home and study rather than to get a part-time job. Teens, in turn, seem to be content with this homebody arrangement—not because they’re so studious, but because their social life is lived on their phone. They don’t need to leave home to spend time with their friends.

If today’s teens were a generation of grinds, we’d see that in the data. But eighth-, 10th-, and 12th-graders in the 2010s actually spend less time on homework than Gen X teens did in the early 1990s. (High-school seniors headed for four-year colleges spend about the same amount of time on homework as their predecessors did.) The time that seniors spend on activities such as student clubs and sports and exercise has changed little in recent years. Combined with the decline in working for pay, this means iGen teens have more leisure time than Gen X teens did, not less.

In this, too, she is typical. The number of teens who get together with their friends nearly every day dropped by more than 40 percent from 2000 to 2015; the decline has been especially steep recently. It’s not only a matter of fewer kids partying; fewer kids are spending time simply hanging out. That’s something most teens used to do: nerds and jocks, poor kids and rich kids, C students and A students. The roller rink, the basketball court, the town pool, the local necking spot—they’ve all been replaced by virtual spaces accessed through apps and the web.

You might expect that teens spend so much time in these new spaces because it makes them happy, but most data suggest that it does not. The Monitoring the Future survey, funded by the National Institute on Drug Abuse and designed to be nationally representative, has asked 12th-graders more than 1,000 questions every year since 1975 and queried eighth- and 10th-graders since 1991. The survey asks teens how happy they are and also how much of their leisure time they spend on various activities, including nonscreen activities such as in-person social interaction and exercise, and, in recent years, screen activities such as using social media, texting, and browsing the web.

There’s not a single exception. All screen activities are linked to less happiness, and all nonscreen activities are linked to more happiness. Eighth-graders who spend 10 or more hours a week on social media are 56 percent more likely to say they’re unhappy than those who devote less time to social media. Admittedly, 10 hours a week is a lot. But those who spend six to nine hours a week on social media are still 47 percent more likely to say they are unhappy than those who use social media even less. The opposite is true of in-person interactions. Those who spend an above-average amount of time with their friends in person are 20 percent less likely to say they’re unhappy than those who hang out for a below-average amount of time.

The more time teens spend looking at screens, the more likely they are to report symptoms of depression.

If you were going to give advice for a happy adolescence based on this survey, it would be straightforward: Put down the phone, turn off the laptop, and do something—anything—that does not involve a screen. Of course, these analyses don’t unequivocally prove that screen time causes unhappiness; it’s possible that unhappy teens spend more time online. But recent research suggests that screen time, in particular social-media use, does indeed cause unhappiness. One study asked college students with a Facebook page to complete short surveys on their phone over the course of two weeks. They’d get a text message with a link five times a day, and report on their mood and how much they’d used Facebook. The more they’d used Facebook, the unhappier they felt, but feeling unhappy did not subsequently lead to more Facebook use.

This doesn’t always mean that, on an individual level, kids who spend more time online are lonelier than kids who spend less time online. Teens who spend more time on social media also spend more time with their friends in person, on average—highly social teens are more social in both venues, and less social teens are less so. But at the generational level, when teens spend more time on smartphones and less time on in-person social interactions, loneliness is more common.

So is depression. Once again, the effect of screen activities is unmistakable: The more time teens spend looking at screens, the more likely they are to report symptoms of depression. Eighth-graders who are heavy users of social media increase their risk of depression by 27 percent, while those who play sports, go to religious services, or even do homework more than the average teen cut their risk significantly.

Teens who spend three hours a day or more on electronic devices are 35 percent more likely to have a risk factor for suicide, such as making a suicide plan. (That’s much more than the risk related to, say, watching TV.) One piece of data that indirectly but stunningly captures kids’ growing isolation, for good and for bad: Since 2007, the homicide rate among teens has declined, but the suicide rate has increased. As teens have started spending less time together, they have become less likely to kill one another, and more likely to kill themselves. In 2011, for the first time in 24 years, the teen suicide rate was higher than the teen homicide rate.

Depression and suicide have many causes; too much technology is clearly not the only one. And the teen suicide rate was even higher in the 1990s, long before smartphones existed. Then again, about four times as many Americans now take antidepressants, which are often effective in treating severe depression, the type most strongly linked to suicide.