LONDON -- An estimated 700,000 girls aged 10 to 15 feel unhappy about their appearance and one-in-seven girls are not content with their lives overall, a new UK report has revealed.

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According to The Good Childhood Report 2016, published by the Children's Society, girls are "less happy than they used to be" about their appearance and a gender gap is also emerging on how young people perceive themselves.

More than one-third of girls in the UK are unhappy with the way they look -- a 30 percent rise over five years. However, the proportion of boys of the same age who are unhappy with their appearance has remained the same, at 20 percent.

The number of boys who are unhappy with their lives as a whole has remained stable at 11 percent, while the proportion of girls has increased from 11 percent to 14 percent over a five-year period.

"The reasons for the widening gender gap are unclear, but the report does find that emotional bullying, such as name-calling -- which girls are more likely to experience -- is twice as common as physical bullying, which is more likely to affect boys," reads a statement on the findings.

"Girls feel pressured by the boys to look a particular way."

One teenage girl who participated in the report suggested young people are feeling burdened by the expectations of peers and family members.

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"There are so many pressures from your friends, from your family. You don’t know who you are going to be, you are trying to find who you are in a certain way," she told the Children's Society.

"Girls feel pressured by the boys that they should look a particular way and that leads girls into depression or low self-esteem and makes girls feel ugly or worthless," said another teenage girl who took part.

Is social media to blame?

Leading children's charities believe this pressure stems largely from social networking.

“Social media puts enormous pressure on young girls to live their lives in the public domain, to present a personal ‘brand’ from a young age, and to seek reassurance in the form of likes and shares," YoungMinds’ media and campaigns manager Nick Harrop said in a statement sent to Mashable.

Harrop said the figures in the report are "yet further evidence that excessive use of social media can have a negative effect on young girls’ self-belief and body image", but concedes that social media can also have its social and emotional benefits.

"[Girls] are under constant pressure, particularly from social media, to attain a certain image, which is often unrealistic," said a spokesperson for children's charity NSPCC in a statement sent to Mashable.

Research conducted by the Office for National Statistics found that girls were far more likely than boys to spend more than three hours on social media sites. Studies have also associated too much time spent in front of screens with reduced feelings of social acceptance and increased feelings of loneliness.

Researchers also consider girls to be more at risk of comparing themselves with other people -- be it online or offline -- and that a lack of self-esteem lies at the heart of this.