Social media is helping fuel a nation of "deeply unhappy" children, a charity has warned, as it published new figures showing a rise in self-harm.
Data obtained under the Freedom of Information Act by the National Society for the Prevention of Cruelty to Children (NSPCC) found 18,778 children aged 11 to 18 were admitted to hospital for self-harm in 2015/16.
This is up on the 16,416 in 2013/14 and represents a 14% rise, the data for England and Wales shows.
Teenagers aged 13 to 17 were the most likely to end up in hospital for self-harm, including things such as cutting, overdosing on pills or burning themselves.
Figures from the Childline helpline run by the NSPCC also showed it delivered 18,471 counselling sessions about self-harm last year - equivalent to 50 a day.
Peter Wanless, chief executive of the NSPCC, said: "A frightening number of children and teenagers are being driven to self-harm as a way of dealing with unresolved feelings, tensions and distress in their lives.
"Knowing hospital beds are full of young people crying out for help should be a real wake-up call to all those that care for the wellbeing of the younger generation.
"It is vital we confront the fact that an increasing number are struggling to deal with the pressures and demands of modern-day life, to such an extent they are inflicting terrible damage upon themselves.
"It is clear from the thousands of calls Childline receives that we have a nation of deeply unhappy children.
"We know this unhappiness is partly due to the constant pressure they feel, particularly from social media, to have the perfect life or attain a certain image which is often unrealistic.
"They tell us that the need to keep up with friends and the 24/7 nature of technology means they feel they can never escape or switch off, adding to the misery that many feel on a daily basis.
"Childline is often the only place that many young people feel they can turn to when no-one else is listening."
Childline president, Dame Esther Rantzen, said: "It is deeply disturbing that so many children and young people are ending up in hospital because they are injuring themselves so seriously.
"Self-harming is at epidemic level among young people - at Childline we hear from them every day.
"It has become one of the most common problems young people bring to us, and I know from our counsellors that these are some of the most painful stories we hear.
"Often the young people feel too ashamed and fearful to seek help from those around them, until they harm themselves so badly they have to be rushed to hospital."
One 14-year-old boy who contacted Childline said: "Sometimes I get flashbacks from what happened when I was younger and I cope with the horrible memories by cutting myself - it helps me release the pain from within.
"School helped take my mind off things but now that the holidays are here I'm struggling.
"My parents always seem to be too busy for me and I don't want to tell my friends what happened.
"I feel so miserable and lonely - can you please help?"
Dr Max Davie, assistant officer for health promotion for the Royal College of Paediatrics and Child Health (RCPCH), said: "Early intervention is essential if we are to reduce the number of children self-harming and needing specialist mental health or emergency services.
"One way of providing this early intervention is for all schools to deliver comprehensive Personal Social Health Economic (PSHE) education, teaching children about emotional wellbeing and addressing challenging mental health issues such as eating disorders, self-harm and suicide in addition to other important topics like positive relationships, sex education and the dangers of drugs and alcohol abuse."
Dr Virginia Davies, chairwoman of the child and family public engagement board at The Royal College of Psychiatrists, said: "The NSPCC's report highlights the real-life impact of underfunded mental health services for children and young people.
"Our own research shows that over half of England's clinical commissioning groups are allocating under 5% of their mental health budget to this age group.
"We also know that up to four in five children with mental health problems are being denied access to treatment they urgently need in some parts of England, despite the evidence that early intervention can prevent a multitude of problems later in life.
"Now more than ever we need more doctors to train as psychiatrists if we are ever to meet the increase in demand for these services."
A Department of Health spokesman said: "We want children with mental health problems to get the help they need.
"That's why we are investing £1.4 billion to help every area in the country transform services for young people with all mental health conditions, including self-harm.
"We are also strengthening the links between schools and mental health services, and looking at how to improve services for self-harm in the reinvigorated suicide prevention strategy, to be published soon."
The NSPCC has a Call for Help campaign to raise funds for services such as Childline.