Girlguiding UK is launching its first "body confidence" badge on Thursday in response to what it says is a crisis in how girls perceive themselves.

The charity believes girls are under intense pressure to look a certain way and hopes courses designed to unmask beauty myths, expose airbrushing and challenge unhealthy body talk will boost their confidence. Girls who complete the training will be awarded a "free being me" badge if they can show that they have taken up the mantle and worked on spreading the message in their schools and communities.

Girlguiding's latest attitudes survey illustrated the extent of concern among young women and girls about body image, with one in five girls of primary school age saying they had been on a diet and 38% of girls aged 11 to 21 revealing they had sometimes skipped meals to help lose weight.

Jenna Nicholls, one of nearly 1,000 peer educators aged between 14 and 25 who are being specially trained to deliver the programme, said: "They are quite scary statistics, as is the fact that people are seeing this as acceptable behaviour.

"I have seen friends go through eating disorders, really suffer from self-confidence issues. It's always there, there's always that constant expectation to look a certain way."

She admitted that it would be a challenge to change attitudes, but said it was important that the training of thousands of seven- to 14-year-olds at Brownie and Guide groups would be conducted by their peers.

The aim is for the message to ultimately reach more than 400,000 girls and young women as those who take the courses are encouraged to become body confidence "correspondents", coming up with their own self-esteem-boosting news stories and spreading the word using posters, video and T-shirts.

The "free being me" badge is a far cry from the days when there were awards for homemaking and milking cows (both since scrapped) and reflects the way in which the organisation has changed in recent years to become what its chief executive has called the "ultimate feminist organisation". Present-day badges include community action, independent living and world issues.

Nicholls said: "Girlguiding is firmly rooted in the 21st century. We are relevant to modern-day girls and that's what makes us so popular."

Chief Guide Gill Slocombe said the charity was committed to helping girls to develop into happy, self-confident young women and the programme would have "a huge impact on the lives of thousands of young people across the UK".

The "free being me" programme is being run in conjunction with the Dove self-esteem project, which aims to improve the self-esteem of girls and young women.