Children who use social media just three times a day are much more likely to have mental health issues, a study suggests.
Scientists analysed data from interviews with 13,000 teenagers that went to more than 1,000 schools across England.
University College London experts found rates of anxiety were 28 per cent higher in teenage girls who used social media more often.
Boys also suffered from scrolling through popular sites such as Facebook, Twitter and Instagram - but not by as much.
Researchers now say it's unlikely flicking through social media sites directly harms mental health.
Instead, they believe spending hours on social media can leave girls vulnerable to cyber bullying, as well as causing a lack of sleep and exercise.
Other factors are thought to be behind the effects of social media on the mental health of boys.
A third of girls who check social media three times a day have mental health issues because they are more exposed to cyber bulling and exercise and sleep less, according to a study
Professor Russell Viner, lead researcher of the study, said: 'Our results suggest that social media itself doesn't cause harm.'
He added that, instead, 'frequent use may disrupt activities that have a positive impact on mental health'.
Professor Viner said: 'I think one of the conclusions is that social media does not displace physical activities in boys in the same way that it does in girls, which may be one of the reasons for this difference that we see.'
The teenagers were quizzed between 13 to 16 at three different time points - 2013, 2014 and 2015.
Very frequent social media use was defined as using networking sites, including WhatsApp and Snapchat, three or more times a day.
In the second year of the study, all of the participants completed a questionnaire which assessed psychological distress,
This term covered a range of different symptoms including sadness, anxiety and difficulty focusing.
Each of the teenagers were also quizzed about their sleep quality, physical activity and if they had been a victim of cyber bullying.
In the third and final year, all the participants were surveyed about their wellbeing, such as life satisfaction, happiness and anxiety.
Use of social media rocketed between 2013 and 2015, according to the findings in The Lancet Child and Adolescent Health journal.
Just 43 per cent of boys and 51 per cent of girls used social media multiple times a day at the beginning of the study.
However, the figures had jumped to 69 per cent and 75 per cent, respectively, by 2015, the researchers discovered.
Very frequent social media use was linked to greater psychological distress in both sexes.
In girls, the more often they accessed or checked social media, the greater their psychological distress.
Some 28 per cent of girls who frequently used social media were distressed in 2014, compared with 20 per cent of those using it weekly or less.
Research has shown spending too much time looking at screens – smartphones, tablets, computers and televisions, for example – can be damaging to children's intelligence, sleep, mental health and vision.