A new study has shown that under-14s believe that the influence of magazines, websites and friends telling them to look and act sexually is making them unhappy, and driving some of them to self-harm and eating disorders.
It has shown that girls as young as ten are suffering from stress and anxiety as they struggle to cope with growing up in today's society.
During the study, conducted by Girlguiding UK, researchers found that pressure to own the latest must-haves such as fashionable clothes; iPods and mobile phones left one in five of them feeling angry or sad.
The report, A Generation Under Stress?, is based on an online survey of 350 Girl Guides aged below 15, together with detailed interviews conducted with teenagers across the country.
Dr Andrew McCulloch, of the Mental Health Foundation, which jointly carried out the study, has accused adults of creating a world of materialism and premature sexualisation.
"Girls and young women are being forced to grow up at an unnatural pace in a society that we, as adults, have created," The Sun quoted him, as saying.
"It's damaging their emotional wellbeing. We have a responsibility to put this right," he added.
For many of the 400 girls surveyed, bullying, exam stress and family turmoil made matters worse.
Researchers found 50 percent knew someone who has suffered depression and two-fifths knew a person who has self-harmed.
Many girls said that self-harming was so common - particularly among those who want to be part of the 'emo' music scene - that it is seen as just another part of being a teenager.
One in three had a friend with an eating disorder and two in five knew someone who had panic attacks.
Liz Burnley, of Girlguiding UK, who was involved in the study, said: "Young girls face a new generation of pressures that leave too many suffering stress, anxiety and unhappiness.
"All of us who care about young women have a part to play in helping them find a way through these conflicting demands to build the confidence they need to be themselves," she added.