The Girlguiding Girls’ Attitudes Survey 2015 also found that 62 per cent of girls aged 11 to 21 know a girl or young woman who has experienced a mental health issue.
But despite many needing help, the study found that they often do not receive adequate support. Fewer than half (44 per cent) of girls aged between 11 and 16 said that they have talked about mental health during lessons at school.
Meanwhile 53 per cent said they do not know enough about mental health issues that affect young people, and 52 per cent said that they would like to know more about where to get help and support for mental health issues.
The study, which featured responses from 1,574 girls, found that mental wellbeing worries start from as young as seven and escalate as they get older, with two in five girls aged 11 to 21 needing to seek help with mental health concerns.
The study also found that self-harming tops a list of health concerns for girls aged between 11 and 21, closely followed by smoking, mental illness, depression and eating disorders.
In 2010, girls’ top three health concerns were binge drinking, smoking and drug abuse.
Girlguiding UK said the mental wellbeing and resilience of UK girls is "under threat".
Julie Bentley, Girlguiding chief executive, said: “We need the support of decision makers to start an open conversation about girls' concerns,” she said.
“By listening to girls, we can work together to tackle the root causes of their distress – and champion their potential.”
