It’s hard to find an American girl or woman who isn’t familiar with Cinderella, Jasmine, Pocahontas, or Mulan.
Yet these characters, collectively known as the Disney princesses, may not be the best role models for young girls, according to a new study by Brigham Young University family life professor Sarah Coyne.
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Coyne looked at the behaviors of 198 pre-schoolers and measured how much they interacted with Disney’s (DIS) “princess culture”—playing with the dolls, watching the movies, etc. She found that a full 96% of girls (and 87% of boys) had viewed at least some princess media. Coyne then observed the children’s behavior a year later and discovered a trend: The more the kids watched and played with princesses, the more likely they were to display stereotypically female behavior.
“We know that girls who strongly adhere to female gender stereotypes feel like they can’t do some things,” Coyne said in a statement. “They’re not as confident that they can do well in math and science. They don’t like getting dirty, so they’re less likely to try and experiment with things.”
The effects also extend to body image—those girls that engaged the most with princess culture over time had the lowest body esteem. “Disney Princesses represent some of the first examples of exposure to the thin ideal,” Coyne said. “As women, we get it our whole lives, and it really does start at the Disney Princess level, at age three and four.”
A 2013 study by the Dove Self-Esteem Project revealed that nearly half of girls between 11 and 14 refused to take part in activities that displayed their bodies in any way (such as swimming or performing on stage).
Interestingly, the effect is dramatically different for boys. According to the Coyne, the boys who engaged with Disney Princess media had higher self esteem about their bodies and were more helpful to others. One possible explanation: The princesses help counterbalance the impact of the super masculine toys and media (think superheroes or war toys) usually given to boys.
Fortune has reached out to Disney for comment and will update this story if the company responds.