Teenagers are more likely to lie, fight and behave badly on days when they have spent a lot of time on electronic devices.
Children aged 11 to 15 struggle more with behaviour and attention spans after activities such as playing computer games and going on social media, a US study found.
Those with existing concentration and behaviour problems become less self-controlled. Experts believe it is because technology encourages children to flit between tasks which makes it harder for them to focus in the real world.
The negative effects of mobile phones – which teenagers use to send an average of 41 messages a day – may then lead to lying and fighting.
Professor Candice Odgers, a co-author of the study led by Duke University, North Carolina, said: ‘Our brains get a hit of dopamine when we receive a text, or other novel information on our phone.
‘Adolescents are especially sensitive to reward, and may be even more distracted by their daily technology use.
‘The same-day link between higher technology use and antisocial behaviour could reflect cyber bullying or negative experiences online which then influence offline behaviours.
"This suggests technology use may amplify existing risks among teens already experiencing problems with behaviour.’
The researchers asked 151 children to complete surveys on smartphones about their daily digital technology use. They were surveyed three times a day for a month and assessed for mental health symptoms 18 months later.
The children, already at a higher risk of behavioural issues, spent an average of 2.3 hours a day using digital technologies – more than an hour of that spent texting.
The researchers found that on days when the youngsters used their devices more, both exceeding their own normal use or the average for their peers, they were more likely to experience conduct problems such as lying and fighting.
The research, published in the journal Child Development, found they had more symptoms of attention deficit hyperactivity disorder on these days, although they were less likely to report symptoms of depression and anxiety.
Odgers said: ‘It may be that children over-using technology is a symptom of existing problems with attention or that... phones are a source of distraction and reward for young teens.’
A follow-up study of more than 2 000 teenagers is now being carried out to understand why digital devices may pose a risk to mental health.