Girls are more likely to have concerns about their appearance than boys as they return to school after the summer holidays, with children becoming more anxious as they get older.
The survey, commissioned by the Be Real Campaign, found that just over one in four (26%) of the secondary age youngsters questioned said their appearance is one of the biggest worries about going back to school.
This is a higher proportion than those that were concerned about making friends, bullying, and getting in trouble, but less than the proportions that were worried about exams, homework, having new teachers and new subjects and classes.
The poll also found that of those, nearly a third (31%) of girls said they were worried about their appearance, compared with 21% of their male classmates, while over 36% of 16-year-olds said they were concerned about this compared with 17% of 11-year-olds
Youngsters were asked if they had any concerns about specific parts of their appearance as they return to school.
The most common answer was spots, freckles and bad skin, followed by body shape and clothes.
The Be Real Campaign was founded by youth charity YMCA and Dove.
Denise Hatton, chief executive of YMCA England & Wales, said: "Young people are constantly bombarded with images of unrealistic body types in the media, advertising and online, which can have devastating effects on their confidence and overall well-being.
"We know that some young people are so worried about their looks that it stops them from raising their hand in class or taking part in school activities, including PE.
"Schools are uniquely placed to support young people to hold positive discussions around body image with their peers and help reduce the negative impact low body confidence can have.
"In this digital age, it's now more important than ever that we talk openly about body image, so that young people can feel comfortable in their skin and have one less thing to worry about when they are going through puberty, which is already one of the most difficult stages of their life."