IT’S become such a common sight that it barely merits comment any more: a group of young people sharing the same physical space, but with every pair of eyes glued to a phone.

Adults may shake their heads in despair at the lack of social grace, but increasingly they have more serious concerns too. Being permanently plugged into WhatsApp, Snapchat and Facebook isn’t just a cause of rudeness, it’s a health hazard too. Glance at the headlines and you’d be forgiven for thinking most teenagers were just a few clicks away from a nervous breakdown.

This week academics warned that surges in screen time for children as young as 11 were storing up problems for later life, including obesity, diabetes and mental ill-health. It’s the last of these that has gained the most attention in the past couple of years, thanks in large part to a study by researchers from the University of Glasgow.

No-one believes that social media use is a direct cause of obesity, with every emoji an empty calorie. Instead there’s an obvious link between online activity and being sedentary, and therefore missing out on exercise. But when it comes to mental health, a media-fuelled moral panic has many concluding that digital connectedness is in itself harmful, with cyber-bullies lurking around every corner and teens desperate for approval pouting for non-stop selfies.

To many hand-wringers, it just doesn’t seem healthy. Surely all this sharing, liking and instant messaging is producing a generation of shallow, narcissistic young people with fragile egos and no sense of the world beyond their own bubbles?

It seems some adults have forgotten that adolescents, as a group, have always been this way. How many children of the 1980s and 90s regularly spent hours talking on a landline phone to friends they’d just spent the school day with? How much time was spent sculpting hair into gel-coated “curtains”, or carefully applying and reapplying lipstick (Bon Bon by Seventeen for everyday wear, naturally, and Rimmel’s Heather Shimmer for a sophisticated evening look).

How many wrote (and perhaps even illustrated) elaborate journals instead of watching the Nine O’Clock News with their parents? How many gathered in streets, parks or each other’s homes to talk about bands, clothes, crushes and petty grievances? To hear some adults talk now, you’d think they’d spent every lunchtime hosting Cafes Philosophiques in the school playground.

There are two main differences today: firstly, young people are creating vast digital profiles that may prove tricky to scrub away in years to come; and secondly, they are connected to each other around the clock.

These connections aren’t just maintained from dusk til dawn, but through the night as well. A 2010 study found 86 per cent of adolescents slept with their phones in their bedrooms, often under their pillows or even in their hands, meaning their sleep was easily disrupted by incoming messages and social media alerts. No wonder teenage pregnancies have declined if this is young people’s idea of a fun night in.

The later Glasgow study by Dr Heather Cleland Woods and Holly Scott, for which nearly 500 Scottish young people were surveyed, broke new ground. It paid particular attention to “emotional investment in social media” – characterised by a fear of missing out (FOMO) when disconnected – and night-time-specific use. It will probably surprise no-one to learn that high levels of each were associated with “poorer sleep quality, lower self-esteem and higher anxiety and depression levels.” So far, so straightforward – an obsession with social media is bad for young people’s mental health, right?

Maybe, but that’s not actually what the evidence shows. A key factor here – perhaps the key factor – is sleep. It’s long been recognised that screen-time late at night is bad for children, because it interferes with melatonin production and disrupts circadian rhythms, but that didn’t stop millions of parents from buying TVs for their offspring’s bedrooms. These days no such fixed equipment is required, as young people have tablets and laptops on which to watch TV, and parents seem resigned to in-bed viewing as a fact of life.

There’s no point telling young people social media is bad for them – they are savvy enough to realise this simply isn’t the case. While it’s commonly believed that viewing a steady stream of picture-perfect images and enviable status updates has a crushing effect on self-esteem, there’s evidence to suggest viewing one’s own profile can have the opposite effect. And while the phenomenon of cyber-bullying makes for alarming headlines, the online world can also be a safe haven for those who don’t fit in so well locally, offering the chance of online connections and real-life friendships based on shared subcultures and interests.

The key factor here is sleep disruption, whichin itself contributes to anxiety, depression and low self-esteem among teenagers, as well as impairing their ability to learn and the likelihood that they’ll get exercise during the day. The problem may not be social media use itself, but the specific temptation it presents to stay online around the clock.

So what’s the answer? A digital curfew may seem draconian, but if all parents were to enforce one there’d be nothing new to miss out on, and the night-time FOMO arms race would cease. Perhaps in its place a healthy daytime FOFA – fear of falling asleep – would inspire young people to log off for their own good.