She'd spent her childhood longing for puberty, but the time she was a teen, the Modern Family star says she felt her breasts were "too big."
"Being a 5-ft.-tall girl and having extremely large breasts is really ostracizing and excruciatingly painful," Winter says in this week's issue of PEOPLE. "But I didn't really express how I felt about that."
"I'd just be wearing something anyone else could wear, but I'd read comments saying, 'She dresses inappropriately,' " she says.
Winter admits she was "hurt" by the online bullying, but it was ultimately the physical pain that led her to decide to undergo breast reduction surgery shortly after becoming an emancipated minor last year.
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"I think it will be the only [cosmetic surgery] I'll have done, but I'm extremely happy with the decision I made,” Winter says of going from a size 32F to a 34D. "It's important to talk about it because there are young girls suffering like I did, but there shouldn't be a stigma about it."
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"It was an instant weight lifted off my chest – both literally and figuratively," she says with a laugh about the surgery. "There's a confidence you find when you finally feel right in your body."