R-Cup OnlyFans Model Says 'No' to Breast Reduction Despite Growth Condition

Summer Robert says her boobs have been massive all her life ... and while that used to make her feel bad about herself, now she doesn't think she'd trade her funbags in for a smaller size.

We spoke with the Scottish OnlyFans model on "TMZ Live" Thursday ... and she told us about doctors recently diagnosing her with macromastia -- a rare disorder that causes excessive breast growth.

Summer is just 4'11" ... but she wears an R-cup bra -- and she admits her buxom bosom makes it hard to do everyday tasks.

Summer says her breasts started growing when she was just 8 ... jumping up to a C-cup virtually overnight. She says she's gone to doctors in the past ... but because her body mass index is thrown off by the weight of her breasts, medical professionals in Great Britain have refused to operate on her.

While Summer says she used to feel super uncomfortable in her own skin -- disliking the near-constant attention -- OnlyFans has made her realize she's unique and beautiful.

So even if a doctor could assure her a breast reduction would solve the growth issue -- Summer says she still wouldn't do it.