Students who are bullied at school are mostly taunted about their weight or body image.
Researchers from DCU also found that teens are reluctant to report incidents of bullying to school staff.
They interviewed 418 students from Catholic all boys and girls schools and also from a mixed community school.
DCU's Dr. Debbie Ging says they were quite surprised to find that body type was cited by the students as the predominant cause for bullying, and that was across the board in all three schools.
Dr. Ging said teachers felt social media played a key factor in this - the selfie culture meant students constantly felt the need to "self-promote" and live up to impossible body ideals.