Nearly one in four young women has a mental illness, with emotional problems such as depression and anxiety the most common, figures for England show.
The official NHS report found young women aged 17 to 19 were twice as likely as young men to have problems, with 23.9% reporting a disorder.
Problems are less common in younger age groups, but are rising, albeit slowly.
In children aged five to 15, one in nine had a disorder, up from one in 10 when the review was done 13 years ago.
The findings are based on a survey of more than 9,000 young people.
The results have been gathered by statistics body NHS Digital and assessed by experts to try to ensure only diagnosable conditions are included.
Dr Bernadka Dubicka, of the Royal College of Psychiatrists, said the numbers of young women with problems was “alarming”.
She said body image pressures, exam stress and the negative effects of social media may all affect girls disproportionately, while they were also more likely to be victims of abuse and sexual assault.
“We can only speculate. We still do not fully understand this – all we know is that we see more girls in our clinics.
“We have to make sure services are available for them.”
It comes as the Children’s Commissioner for England warned there was a “vast gap” in NHS mental health support.
Anne Longfield’s report criticised slow progress made in improving specialist community services for children.
She said waiting times were too long and she was concerned about numbers being rejected by services in some areas.
Nearly half of those in their late teens with mental health problems had self-harmed or attempted suicide. For younger teens it was about a quarter.
‘I’ve missed so much of my life’
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Emma Blezard, 18, says her mental health problems have robbed her of her teenage years.
She started experiencing difficulties when she was 13, suffering from anxiety and panic attacks before developing an eating disorder.
It was a year before she let on to her parents. She ended up having suicidal thoughts and was sectioned in hospital at one point.
“I’ve missed so much of my life because of this illness – I’ve lost friends, I’ve missed birthday, holidays.
“I wish I could do things over.”
Even when she was receiving treatment, she felt she did not deserve it.
“I became really isolated. At school I spent a lot of time out of lessons with the nurse. It was very difficult.”
She has travelled all over the country for treatment and says she still struggles, although her problems are more manageable now.
“I don’t think they will ever go away.”
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Is social media to blame for problems young people face?
It may be a factor, although it is hard to tell.
The NHS Digital review found children aged 11 to 19 with a mental health problem were more likely to use social media.
Nearly a third of them spent over four hours a day on social media.
Those who did not have a mental health problem were two to three times less likely to spend that amount of time on it.
The young people with mental health problems were more likely to say their mood was affected by the number of “likes” they got and they were also more likely to compare themselves to others on social media.
The report cited cyber-bullying as an issue too.
But while this does suggest social media can have a negative impact, it does not prove it is to blame.
People with mental health problems may be just more likely to find themselves on it, rather than it causing their problems in the first place. Indeed, they could even be using social media for support.
Adolescence is key
The majority of problems reported, particularly in the older age groups, are linked to emotional disorders.
These are on the rise, whereas the other disorders they looked at – behavioural and hyperactivity – have remained relatively stable over time.
University College London psychiatrist Dr Michael Bloomfield said: “Adolescence is a critical period for a person’s development, particularly as our brains go through important changes during our teenage years.
“Since prevention is better than cure, it is really important for all of us in society to understand together why this is and start reducing the rates of mental disorders in young people.”
How many children get help?
The NHS is only treating a fraction of the young people who have problems.
The Children’s Commissioner’s analysis of NHS figures from 2017-18 show that 325,000 children were treated by community services, while there are another 5,000 in hospital.
That is fewer than 3% of the population.
The figures showed that more than a third of young people referred to community services were turned away.
This could be because their needs were not severe enough to need help and could be dealt with through other services, such as in school or by charities and council social care teams.
But Ms Longfield said she was concerned children were getting turned away because services simply did not have time to see them.
Her report also raised concerns about waiting times. Just under half of people who received treatment after a referral in 2017-18 had waited longer than six weeks. The average waiting time was nearly two months.
What needs to happen?
The commissioner believes children’s services are under-funded. Around £700m is spent on child and adolescent mental health services (CAMHS) and eating disorders support.
By comparison, services for adults receive 15 times more despite children representing 20% of the population.
The commissioner said an extra £1.7bn would need to be invested to bring children’s services in line.
She said this could help pay for more early help by funding NHS counsellors in schools for example.
Emma Thomas, chief executive of the Young Minds charity, said there was a lack of support for children.
She said the charity gets “calls every day” about children who are waiting for help or have been denied help.
“This can have devastating consequences – in some cases, children start to self-harm, become suicidal or drop out of school while waiting for the help they need.”
She agreed early intervention and better funding were essential.
What is the government doing?
Both NHS England and the Department of Health and Social Care have made improving children’s mental health care a priority.
In fact, the commissioner’s report noted that investment was increasing and there had been good progress in terms of tackling eating disorders with new services and strict targets for access.
Last month, in his Budget, the chancellor announced at least £2bn of the extra £20bn earmarked for the NHS by 2023 would go on mental health.
A new four-week target for access to CAMHS is also going to be piloted soon and NHS England has promised another 70,000 children will be able to access support in the coming years.
National mental health director Claire Murdoch said the scale of the problem identified by NHS Digital showed the importance of “ramping up” access to services.
She said the NHS long-term plan, due out soon, would set out more details about future investment.
“Everyone who works with children and young people, whether in the public, private or voluntary sector, has to play their part if we are to protect young people’s mental wellbeing.”
Ministers have also being putting pressure on social media firms to do more about cyber-bullying and aggressive behaviour online.
One option being considered is a new regulator for the internet.