If you or someone you know is considering suicide, help is available. Call 1-800-273-8255 to speak with someone now or text START to 741741 to message with the Crisis Text Line.

It’s a cultural stereotype as old as the landline: teenagers love their phones.

But for North American teen girls, especially, increasing smartphone use could have a darker side. Depression and suicide rates in teenagers have jumped in the last decade—doubling between 2007 and 2015 for girls—and the trend suspiciously coincides with when smartphones became their constant companions. A recent study places their screen time around nine hours per day.

Another study, published on Tuesday, suggests that suicide and depression could be connected to the rise of smartphones, and increased screen time. Around 58 percent more girls reported depression symptoms in 2015 than in 2009, and suicide rates rose 65 percent. Smack in the middle of that window of time, smartphones gained market saturation. “Even if we call screen time a neutral and assume it doesn't help or hurt, it may still have a negative impact if it crowds out time for seeing friends in person,” lead researcher Jean Twenge, psychology professor at San Diego State University, told me in an email. “The large and sudden increase in teen mental health deserves attention, no matter what its cause.”

Trends in screen activities, non-screen activities, and depressive symptoms, 8th and 10th graders, Monitoring the Future (MtF), 2009-2015. Image: Jean M. Twenge

Still, other research suggests that using new media to communicate and connect doesn’t hurt teenagers, and can maybe, in some cases, be good for them. Are screens, and especially smartphones, really killing teenagers?

In Twenge’s new study, published in the journal Clinical Psychological Science, the researchers looked at two samples: a nationally representative survey by ongoing study “Monitoring the Future” out of the University of Michigan, which is administered annually to 8th, 10th, and 12th graders, and the Centers for Disease Control’s Youth Risk Behavior Surveillance System, a sample of high school students administered by the CDC every other year. (Both surveys began in 1991.) Altogether, over 500,000 young people were included.

The study authors examined trends in how teens used social media, the internet, electronic devices (including gaming systems and tablets), and smartphones, as well as how much time they spent doing non-screen activities like homework, playing sports, or socializing.

Comparing these to publicly available data on mental health and suicide for these ages between 2010 and 2017 showed “a clear pattern linking screen activities with higher levels of depressive symptoms/suicide-related outcomes and non-screen activities with lower levels,” the researchers wrote in the study. All activities involving screens were associated with higher levels of depression or suicide and suicidal thinking, and activities done away from a screen were not.

As for why young women are especially impacted, Twenge said that it’s possible social media is to blame: girls spend more time on social media, and boys spend more on gaming. Social media may be more detrimental to mental health than gaming, she said.

In general, the research around screen time and its impact on mental health is scant and often conflicting, with other research suggesting that, in some ways, it can be beneficial. Some studies claim certain video games can be therapeutic. Online communities can keep teenagers connected to the world and to peer groups that share their interests or identities—thus avoiding the isolation and loneliness that’s often a precursor to suicidal thoughts. It’s hard at times to sus out what findings are fact, and what are a result of older adults confirming their own biases about a medium they didn’t grow up with, aren’t a part of now, and don’t fully understand.

Twenge’s work has drawn criticism from psychology peers in the past—particularly after her article “Have Smartphones Destroyed a Generation?” appeared in the September 2017 issue of The Atlantic. Psychologist and author Sarah Rose Cavanagh published her rebuttal on Medium, claiming that Twenge’s data is “cherry-picked” to reinforce preexisting biases, and that she falls into the old “correlation versus causation trap” in the conclusions she draws.

Psychologist Andrew Przybylski told NPR that teenagers today might just be more willing to admit when they’re worried or sad, or better equipped to recognize symptoms of depression within themselves.

I asked Twenge what she makes of these criticisms—that her conclusions are alarmist, or over-hyped by the media. “I've seen a few people argue that ‘the kids are just fine,’” she said, “but with 65 percent more teen girls committing suicide in just a five-year period, I can't see how anyone can make that argument, or say that it's ‘overhyped.’” Documenting this increase in reported mental health issues is important, she continued, in order to understand the scope of the problem and help teenagers who might need it.

Lisa Pont, therapist and educator with the Centre for Addiction and Mental Health in Toronto, told me that girls are more likely to use, and have unhealthy relationships with, social media. And much of mental health and internet use comes down to isolation. “It is not uncommon for people who are depressed to socially isolate,” Pont said. “Once isolated, people may be inclined to go online to distract from painful emotions, reduce boredom or meet needs for some kind of social connection.” It becomes a vicious cycle. Depression makes them turn to screens more, in this view, and more screen time may make the depression worse.

Twenge is not advocating for pulling the plug on connected teens altogether. One thing experts can agree on is that there is a limit to how much time spent staring at screens starts to affect mood. Two hours seems to be the cut-off, Twenge said. More than that, and negative effects creep in.