Ariel, who plays Alex Dunphy in the American TV sitcom, made the decision to reduce her 32F cups to 34D after suffering with back and neck pain.
Ariel, who had the surgery in June, told Glamour magazine: "It's amazing to finally feel right. My neck was hurting so bad and I actually had some problems with my spine.
"I had been discussing my chest with doctors for many years, but when I finally said, 'I'm thinking of doing this', he said, 'Your back is going to thank you so much'."
The 17-year-old actress explained how her bigger breasts presented her with wardrobe challenges while filming, saying they had to "hide it" on the show.
"Big sweaters, or strapping me down, which is fine, I understand that it doesn't fit the character they have in mind. I understand that. But it was difficult to do that every day," she said.
Taking to Instagram on Wednesday, Ariel thanked fans and her close friends for their support, before saying: "Always make decisions because YOU want to, and always do what makes YOU happy."
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