Teenage girls say Instagram’s mental health impacts are no surprise.

Annie Zhu got an Instagram account during her freshman year of high school. At first, she curated her profile carefully, showing off different outfits and looks. She followed body positivity and body neutrality accounts. But she still sometimes compared herself with others, and “it can make me feel bad,” she said.

So when she recently listened to a podcast revealing how Facebook’s research concluded that Instagram, which it owns, was toxic for teenage girls, she said, the findings “didn’t surprise me at all.”

“In my past experiences, it has been a huge struggle,” Ms. Zhu, an 18-year-old Stanford University freshman, said in an interview.

Among young people, the idea that Instagram can hurt someone’s self-image is widely discussed. Ms. Zhu said she and her friends talked about how social interactions on Instagram felt inauthentic. Some friends have deleted the app because they didn’t think it was contributing positively to their lives, she added. She said she now used Instagram largely as a messaging system and rarely posted on it.

“If you ask a young person, it’s something you deal with on a daily basis,” said Vicki Harrison, who directs the Center for Youth Mental Health and Wellbeing at Stanford. “You don’t need this research to tell you this.”

Ms. Harrison works with the GoodforMEdia project, a peer mentoring initiative for older teenagers and young adults to share experiences and advice on using social media. Teenagers she works with have told her that Instagram is often the hardest platform for them because of how polished users’ social media profiles are.

Their experiences were echoed in Facebook’s internal research. Documents that a whistle-blower, Frances Haugen, provided to The Wall Street Journal showed that Instagram made body-image issues worse for one in three teenage girls.

Facebook has responded that the research did not show a causal link and that a majority of teenage girls experiencing body-image issues reported that Instagram either made their body image better or had no impact.

Iris Tsouris, a freshman at Yale University, said Instagram had worsened her body image issues. While she follows some body positivity accounts, that kind of content doesn’t show up in the algorithm-curated posts on her Instagram Explore page — where she instead sees posts about replacing meals with iced coffee.

Facebook’s research was “not at all” eye-opening to her, she said.

“It perpetuates negative self-image in people, stuff that might feed into eating disorders,” Ms. Tsouris, 18, said. “I’ve definitely seen people impacted by jealousy or the fear of missing out.”

Still, some teenagers said they were glad the research was out, even if they were not sure what it would change.

“The fact that Facebook knows is important,” said Claire Turney, 18, a freshman at the University of Virginia who attended high school with Ms. Tsouris. “That they know that it is destructive and they continue to market it to teenage girls is a little messy in my opinion, but that’s capitalism.”