As researchers begin to investigate how boys and girls use their devices, clear differences are emerging - some of them dramatic. Here’s what we know.

In general, studies have shown that girls spend more time on social media, and boys more time online gaming and watching TV. That won't surprise you! But what may is that small difference makes a big difference when it comes to wellbeing.

In a nutshell, gaming has been shown to be less harmful to kids’ mental health than social media. 

Research published in the journal Social Psychiatry and Psychiatric Epidemiology last year found the time teens spent on social media and internet use was more strongly associated with self-harm behaviors, depressive symptoms, low life satisfaction, and low self-esteem than hours spent on electronic gaming or watching TV. 

Overall girls appear to be more at risk of screen-time-related mental health harms than boys. Among girls, heavy internet users were 166% more likely to show symptoms of clinical depression than low users among girls, compared to 75% more likely among boys.

A global study of more than 577,000 kids aged  11 to 15 and published recently in The Lancet found detrimental mental health impacts start after two hours of screen use for girls and after four hours for boys.

A 2021 study of eight- and nine-year-olds by Irish researchers found that boys, on average, clocked up significantly more screen-time than girls did - an average of three hours a day compared to just over two for girls. Other studies in different countries have shown similar results. 

Overall girls appear to be more at risk of screen-time-related mental health harms than boys.

But the Irish study also found that boys were also more physically active than girls, and researchers speculated that may moderate the wellbeing impact of that extra hour. 

For both boys and girls, the study found “an inverse relationship between total screen-time and reported wellbeing.” In other words, as screen-time increased, wellbeing decreased.

But the most alarming findings, and also the most recent, investigated the link between early screen-time and autism.

The Japanese study, published last month in JAMA Pediatrics, analyzed over 84,000 children. Its shock finding? Among boys, but not girls, longer screen-time at one year of age was "significantly" associated with autism spectrum disorder diagnosis at three years of age.

" ... boys who watched screens two to four hours a day were three times as likely to be diagnosed with ASD at age three ..."

It is well known that boys are three times more likely to be diagnosed with autism spectrum disorder (ASD) than girls. But this study compared boys with boys as well as boys with girls.

Specifically, it found boys who watched screens two to four hours a day were three times as likely to be diagnosed with ASD at age three, compared to boys who watched less than an hour.

In Japan, as in many other developed countries, device use among very young children has been normalised. According to a survey conducted by the Cabinet Office in Japan, 85.7% of children younger than one year and 75.7% of 1-year-old children were using mobile phones, and many of them shared mobile phones with their parents.

But does screen-time actually increase boys’ susceptibility to ASD, or do some boys simply gravitate to screen-time because they are more susceptible? It’s an issue scientists refer to as “reverse causality.” In this case, researchers made an effort to control for variables that have been shown to pre-dispose kids to ASD.

As to the question why screen-time was affecting young boys so dramatically, researchers speculated about the impact of electromagnetic fields on developing brains.

“In particular,” they noted, “in infancy when neurodevelopment is active, environmental factors such as electrical stimulation through screens and light stimulation from vision may affect neurodevelopment and de novo sequence alterations.”

The study authors concluded that, for boys, “Limiting screen time to no more than one hour per day, at least until age one, reduces the environmental risk of ASD.” But they stressed that screen-time was one of a number of environmental factors that appear to be influencing the onset of the disorder.