Most teenagers today grow up with a phone in their hand. They scroll before school, between classes and late into the night, and parents often wonder what all that time is doing to them.
For years, no one could give a clear answer. A new Australian study now offers one, and it is calmer and more careful than most of the warnings we hear.
A decade-long study of teens
Researchers at the Murdoch Children’s Research Institute (MCRI) and Deakin University followed almost 1,200 young people in Melbourne for more than 10 years.
The teenagers joined the Child to Adult Transition Study (CATS) at age eight or nine and answered the same questions every year.
Each year, the teens shared how long they spent on social media and how they were feeling.
The team then checked whether heavy use in one year led to more mental health problems the next.
Their screens slowly filled more of the day. By ages 17 and 18, about half of the girls used social media for more than two hours a day, and most boys did too.
The depression link
The strongest finding was about depression.
Teenagers who spent more than two hours a day on social media were more likely to feel low a year later than those who used it for under an hour.
But the effect was small. For every 100 heavy users, about five more felt seriously down compared with the lightest users.
Well-being showed the same gentle dip. Anxiety and self-harm, on the other hand, barely moved.
The averages hid something important. Once the researchers looked at boys and girls separately, the risk for girls was about twice as large.
Girls who spent more than two hours a day online clearly felt worse, and even one to two hours was enough to show up. For boys, the numbers stayed close to zero.
Impacts in early adolescence
Age turned out to matter even more than the hours.
The sharpest effects showed up in girls aged 12 and 13, right at the start of their teenage years.
In that group, heavy use was tied to about 12 extra girls in every 100 feeling low or unhappy.
Older girls faced about half that risk, and even moderate use hurt the well-being of the youngest.
“Early adolescence stands out as a time when higher levels of social media use are linked to a greater risk of mental health problems one year on,” said Dr. Nandi Vijayakumar of MCRI and Deakin University.
Why early teens struggle
Several things pile up at this age. Girls usually reach puberty a year or two before boys, and the part of the brain that handles strong feelings is still growing.
All of this happens just as they open their first accounts and meet comparison, conflict and unkind content.
Around the same age, girls also begin to report more depression and anxiety than boys, a pattern seen for decades.
A British study found much the same thing. Girls aged 11 to 13 who used social media more reported feeling less satisfied with life a year later, while older teenagers showed no such change.
The key time to intervene
A jump of five in 100 might sound tiny. But spread across millions of teenagers, even a small risk reaches a huge number of young people.
The researchers counted real cases rather than abstract scores. That makes their results easier to use when leaders ask how many teenagers a new rule would actually help.
“While the increases in risk were modest in our study, even small effects can have important public health implications when large numbers of young people are exposed,” said Dr. Vijayakumar.
“This is why early adolescence may be the key time to intervene.”
The results arrive in the middle of a fierce debate. Australia recently passed a world-first law limiting social media for younger teenagers, and the findings speak straight to it.
“Concerns about the impact of social media on adolescent mental health have fueled community and policy debates globally and driven Australia’s world-first social media legislation,” said Professor Susan Sawyer of MCRI.
“Despite all this, robust evidence of population-level impacts has remained limited, making our findings particularly significant.”
Plenty of teenagers say social media helps them feel connected and express themselves. The study does not ignore that side.
“Our results don’t suggest that social media is universally harmful but it’s not without some harms,” Professor Sawyer said.
“It reinforces the need for age-appropriate limits, better education and literacy programs and clearer parental guidance.”
What we still don’t know
Teenagers often guess low about their own screen time, and the data began in 2014, before some of today’s apps changed how young people scroll.
Furthermore, the study counted hours, not what teens actually did online. So it cannot tell us whether watching others feels different from posting and chatting.
It also lumped all heavy users above two hours together, which may hide differences among the busiest scrollers.
Put together, the message points away from panic and toward care.
The biggest gains, the authors say, may come from protecting the youngest teenagers, especially girls, during one short and tender stretch of growing up.
That could mean sensible time limits, better lessons about life online, and more support for parents, rather than one blunt rule for everyone.
The evidence is modest, yet it points to a clear place to start.
The study is published in the Medical Journal of Australia.
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