BACKGROUND: Adolescent girls appear more vulnerable to experiencing mental health difficulties from social media use than boys. The presence of sexualized images online is thought to contribute, through increasing body dissatisfaction among adolescent girls. Sexual objectification through images may reinforce to adolescent girls that their value is based on their appearance. This study explored how sexualized images typically found on social media might influence adolescent girls' mental health, in positive and/or negative ways. METHODS: In-depth interviews were conducted with girls aged 14-17 years (n = 24) in Perth, Western Australia. Data were analyzed using thematic analysis. RESULTS: Participants identified body image as a major concern, reporting negative appearance comparisons when viewing images on social media. Appearance comparisons were perceived to exacerbate adolescent girls' appearance-based concerns. Comparisons also influenced adolescent girls' efforts to change their appearance and seek validation on social media. The importance of awareness and education from a younger age about social media and its influence on body image was emphasized, as was the need for strategies to promote positive body image and counteract negative body image. CONCLUSION: The findings of this study have important implications for professionals working with adolescent girls and for the development of health promotion programs addressing social media use and body image concerns.