There has been a "rapid" rise in teenage girls self-harming in recent years, experts have found.
Between 2011 and 2014 reports of self-harm among British girls aged between 13 and 16 rose by 68%, according to new research.
Experts from the University of Manchester gathered data from 674 general practices across the UK on the number of children and adolescents aged 10 to 19 years who had self-harmed.
The study, published in The British Medical Journal, found that between 2001 and 2014, 16,912 children and adolescents were identified as having self-harmed at least once.
Of these, almost three quarters (73%) were girls.
For girls, the rate of self-harm was 37.4 out of every 10,000 girls, compared to 12.3 per 10,000 boys.
For girls aged 13 to 16 the rate rose from 45.9 per 10,000 in 2011 to 77.0 per 10,000 in 2014.
The authors said that high rates of self-harm could potentially be due to the emergence of common mental health problems at this age as well as biological factors such as puberty and onset of sexual activity.
They said that reasons behind the increase were speculative but added: "Some evidence indicates that common mental disorders are becoming more common among this age group - perhaps a reflection that today's early adolescents are living in more stressful times."
They added: "Exposure to digital media and its potential impact on children and adolescents' mental health is the centre of continued media debate.
"Such technologies can be helpful and facilitate access to care but there is also a suggestion that extreme 'connectedness' could have detrimental effects."
Overall in about 55% of cases of self-harm, no referral to mental health services was documented.
The authors said that referral rates to psychiatric services were "low" which suggests "less severe cases or possible reflection of the challenges in accessing specialist services in a timely manner".
They found that children living in the poorest areas were 23% less likely to be referred in the year after their self-harm episode when compared with youngsters in the least deprived regions.
The authors also assessed risk of death by comparing 8,638 youngsters who had self-harmed to 170,274 children who had not.
A total of 43 deaths occurred among young people in the self-harm cohort and 176 in the comparison group.
Those who had self-harmed were nine times more likely to die unnaturally - including suicide and accidental death - compared to their peers, they calculated.
They were also 17 times more likely to die by suicide.
Nav Kapur, professor of psychiatry and population health at the University of Manchester, said: "Though the higher rates of self-harm in girls than boys and a strong link with the risk of later suicide has confirmed previous work, perhaps our most striking finding was the apparent rapid increase in self-harm recorded for girls aged 13-16.
"We can't really explain this possible rapid increase in self-harm among girls. It could reflect better awareness or recording of self-harm in primary care.
"But it could also be a result of increasing stress and higher levels of psychological problems in young people.
"There is some evidence indicating that common mental health disorders are becoming more common within this age group.
"The internet and social media can be really helpful in preventing self-harm but could have negative effects too and this is a focus of significant research and activity."
He added: "These results do emphasise the opportunity for earlier intervention in primary care to reduce suicide risk.
"We know talking treatments can help. There is also a need for more integrated care involving families, schools and health and social care providers and the voluntary sector to enhance safety among these distressed young people and to help secure their future mental health and well-being.
"It's very important that young people, parents and carers aren't unduly alarmed by these findings. We know that for many young people things get better and they no longer hurt themselves as adults.
"But of course we must take self-harm seriously; it's important to understand its underlying causes."
The researchers, led by Dr Cathy Morgan, said that self-harm was the biggest risk factor for future suicide - which is globally the second most common cause of death for 10 to 24-year-olds behind road accidents.
An NSPCC spokesman said: "These heartbreaking figures are sadly unsurprising because Childline hears from so many young people who hurt themselves.
"Last year we held more than 15,000 counselling sessions about self-harm, and many young people who talked about suicidal feelings also mentioned self-harm.
"Self-harm can often be an expression of a deeper problem which is why early intervention services to support these children are vital.
"Without this, the consequences really can be a matter of life or death."
Tom Madders, campaigns director at the charity YoungMinds, said: "The reasons behind self-harm can be complex, but we know that teenage girls face a wide range of pressures, including school stress, body image issues, bullying and the pressure created by social media.
"Difficult experiences in childhood - including domestic violence, neglect or bereavement - can also have an impact on mental health, sometimes several years later.
"It can take a lot of courage for a young person to tell their GP that they're self-harming, and it's crucial that specialist mental health services are available for all those who need support.
"As a society, we also need to do more to prevent mental health problems from developing in the first place.
"To start with, we need to rebalance the education system, so that schools can prioritise wellbeing and not just academic performance."
Health Minister Jackie Doyle-Price said: "It's worrying to see the number of young people who self-harm and experience suicidal feelings is increasing, I want every young person to be able to seek and access help when they need it.
"That's why we have made the national suicide prevention strategy address self-harm as an issue in its own right for the first time, backed by a record £1.4 billion investment in young people's mental health care, and we're working with schools to provide mental health first aid training, so that all children can get support they need."
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