Concerns about a career, money, housing, education and social media could be fuelling a rise in mental health problems for millennials.
Adolescents feel under more pressure to be successful at school and worry about their job prospects and getting on the housing ladder when they are older.
As the awareness of mental health increases and the stigma declines, more adolescents are admitting they may be suffering from anxiety and depression, according to neuroscientist Sarah-Jayne Blakemore.
"My child psychiatrist and child clinical psychologist friends say there has been an increase in the real prevalence of these conditions and why is the million dollar question," Professor Blakemore said.
"What is it that we are doing now to young people that gives them the increased risk of developing these conditions? No one has the answer."
Prof Blakemore, who is professor of cognitive neuroscience at University College London, told an audience at the Cheltenham Science Festival that smartphones, social media and technology played a part.
"There is a lot of stress about social media and cyberbullying and the need to constantly be in contact and get peer approval right throughout the night," she said.
"Maybe that's a factor."
She said teenagers were having to sit more exams and they had got harder compared to when she did them 20 years ago.
"We have become much more grade focused. Young people feel so much pressure to perform well in the huge number of exams they have to do," she said.
"There must be lots of other things going on, such as exposure to a lot of negative news and now it is right in front of you and you cannot avoid it.
"I wonder what that's doing to young people's brains?
"Also, things like the job market and we are constantly talking about young people never getting on the housing ladder.
"When I talk to teenagers they are very aware of that negativity around them. Maybe it is a whole lot of things in their environment that increases their likelihood of feeling symptoms of anxiety and depression."
Prof Blakemore, a mother of children aged 10 and 13, said her PhD research on schizophrenia in young adults found that patients reported first noticing symptoms before the age of 24.
She also said it appeared more "socially acceptable" to mock teenagers in a way that you would not with other age groups.
"It would be hard to imagine a TV show that was all about mocking elderly people for poor memory and yet we do it with teenagers," she said.
"We also demonise teenagers and are very negative about teenagers and that is not a new phenomenon.
"Adolescent behaviour is fascinating and a fascinating period of life because adolescence is really fundamental to who we are and to the adults we become."
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