When experts talk about screen time, they often focus on the significant developmental impairment too much of it can wreak on small children. But adolescents, who have more control over how they use their time, often are unconcerned with consequences; increasingly, their time is being spent in front of a screen.

And increasingly, there are stories of the impact of this screen time — of the boy who became ‘catatonic’ after playing an online game for too long; of the girl who became depressed after hours on YouTube — even as institutions liberalize recommendations on adolescent screen time. Late last year, the American Academy of Pediatrics (AAP) did away with its two-hour cap of daily screen exposure for adolescents; in fact, it did away with a specific limit entirely (though it recommends families set their own).

Muddying the waters further is the fact that popular conclusions about screen time for adolescents draw from a wide range of studies that have little in common, making it unclear if it is the effect of the screen itself, the activity, both, neither, or something else entirely that impacts adolescent development.

The screen

The only unquestionable way in which screen time — and the vastness that term encompasses — affects adolescents is in the hardware of a device: The light of screens inhibits sleep. Screens emit blue light, which impairs the body’s production of melatonin – the hormone that signals when it’s time to feel sleepy. The longer a person is exposed, the more difficult it can be for them to fall asleep or sleep well.

Most devices now come with a function or app that allows users to filter out the blue light at night, turning the screen a sickly orange colour as ambient light dims. But there’s no proof these are effective in improving sleep. Additionally, some studies point to green light being as disruptive to circadian rhythms as blue in dim environments, perhaps rendering these filters moot.

The problematic effect of this on adolescents is not mere fatigue, but a significantly decreased capacity to learn. For children, through the teenage years, sleep is an essential part of learning; it’s when the brain processes and builds connections based on information taken in during the day. Adolescents, especially, have many obstacles, both physiological and social, to getting enough quality sleep — even without the the blue (or green) light of screen time disrupting their biological clock.

The activity

This is where it gets complicated. Watching TV, playing video games, social media, Googling, even reading on a screen — all of these activities and more are facilitated by screens, all can have very different effects — but those effects aren’t 100% assured for every individual and they’re not necessarily negative.

Binge watching can affect sleep (outside of the blue-light issue) — but so can exercise. Googling, like social media, activates the brain’s reward system and provides instant gratification with Likes, ever-updated newsfeeds, and instant search results — but so does a kind word from a parent, or a snack when hungry. These are natural physiological responses that just happen to be activated by a screen, and science has yet to find consensus on whether that’s better, worse, or no different from other, non-technological stimuli. For every report that playing video games atrophies the brain’s gray matter, there’s a study that has found the brains of players become more efficient at paying attention; for every teenager depressed after hours on social media, there’s another who has found solace and support (#itgetsbetter) in online communities.

Perhaps because of the sheer breadth of screen activities and highly individualized responses to them, we focus on the one thing that can be standardized and, potentially, controlled: time.

The time

Recent research led by psychologist Christopher Ferguson of Stetson University might finally answer how much screen time a teenager should have. The study, published earlier this year, found as many as six hours of screen time daily had no association with a gamut of negative adolescent outcomes like poor health, low grades, risky driving, risky sex, substance abuse or eating disorders.

The real concern most parents have is not necessarily about the amount of time, per se, but a potential total and compulsive disregard for time. In other words: screen addiction.

The scientific community is mixed as to whether screen time is, in fact, addictive. Studies have found that the activation of the brain’s reward center triggered by substance addiction is similar to the stimulus of engaging in behaviours like gambling, shopping, sex, gaming and general Internet use to excess. But as Rachel Becker reported for The Verge last year, “because these are things pretty much everyone engages in, it’s hard to draw a line between one person’s activity and another person’s addiction.” One healthy adolescent’s occasional indulgence can be another’s unhealthy excess.

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For this reason, perhaps, the Diagnostic and Statistical Manual of Mental Disorders, or DSM, the ultimate reference book for the psychiatric profession in the US, identifies drug addiction as a condition (substance use disorder), but does not recognize technology addiction as one. (Interestingly, China does classify Internet addiction as a clinical disorder: Six hours of online time daily with one of the following symptoms in the last three months: a yearning to get back online, mental or physical distress, irritation and difficulty concentrating or sleeping.)

The reason

But parental focus on why a teenager spends their time online might be as important as the length of time they spend staring at a screen or even their activity. And one clue to figuring that out is a look at adolescents’ real-world lives, researchers say.

“We tend to count hours spent using technology, rather than seek to understand the reasons teens are immersed in the digital world,” said Candice Odgers, an associate professor in Duke’s Sanford School of Public Policy, in 2015. Odgers, also the associate director of the Duke Center for Child and Family Policy, is the author of a study that found most parents’ fears about their teens’ digital use are inflated.

Contrary to the early days of the Internet, when a small minority of teens were online and heavy Internet use was a sign of offline problems, now, teens’ online worlds mirror their offline lives. Teens with strong offline social networks tend to reinforce and strengthen their relationships through online interactions, the review found. Rather than connecting with strangers, most adolescents use digital media to interact with friends and acquaintances already in their face-to-face social networks.

“If parents have concerns about their teen’s face-to-face social interactions or activities, they probably have more reason to be concerned about online activities,” said Odgers’ co-author Madeleine J. George.

The way forward

“Each generation worries about how young people are using their time,” Odgers said at the time of the study. “We see young people constantly on their phones and assume ill effects, but much of the research to date tells a more positive story.”

And screen time seems to be the touchstone for fear over this generation, encapsulated in a recent article in The Atlantic, titled, “Have Smartphones Destroyed a Generation?” Unsurprisingly, the author concludes that they are, contributing to rising rates of mental health problems among today’s adolescents. But a swift backlash has followed by other experts, who say the data used to support the assertion is correlational only.

And there’s the rub: When it comes to screen time for older kids, there are a lot of possible effects, some of which are negative, but no body of evidence to tell us explicitly when, why and how these possible negative outcomes occur and what, exactly, is their cause.

What we do know, is that how parents approach children’s technology use plays a big role in how healthily they use technology. Research has found parents tend to fall into three categories when it comes to screen time for kids. Limiters restrict duration and/or type of activity kids can engage in on devices; Enablers allow children to set the digital agenda and follow their lead; and Mentors, who actively engage with their children about and on the Internet and digital devices; these are parents who speak to their children about how to use the Internet responsibly, and/or engage in digital activities with the child, like playing video games together. Alexandra Samuel, the researcher, concludes of Mentors:

That effort seems to pay off. In a survey that asked parents about where their kids get into trouble online, I found that among school-aged kids, children of limiters who are most likely to engage in problematic behavior: They’re twice as likely as the children of mentors to access porn, or to post rude or hostile comments online; they’re also three times as likely to go online and impersonate a classmate, peer, or adult. Shielding kids from the Internet may work for a time, but once they do get online, limiters’ kids often lack the skills and habits that make for consistent, safe, and successful online interactions.

In other words, while there may be no escaping the screen’s blue light, the other effects of screen time on a teenager might be shaped less by the time or activity, and more by how much parents are aware of and involved in their digital adventures.