The former `The Hills` star - who has appeared in numerous bikini photo shoots - has a problem with her chest bone which affects the appearance of her boobs.
When quizzed on whether she`d had breast enhancement surgery, she told iPad news provider The Daily: "I don`t like to talk about that. Well, see I have this chest problem. My bone right here, it`s higher on this side? It`s pectoralis something. So I`ve always struggled with that. You could see they look different sizes all the time."
Audrina admits she gets exasperated with rumours she has had cosmetic surgery and blames her `The Hills` co-star Heidi Montag - who has famously gone under the knife for over 10 procedures, including breast augmentation and a nose job - for the speculation surrounding her appearance.
She added: "I always get asked about that because of Heidi and there`s all these rumours and they all say I`ve had, like, six procedures, and I`m, like, `Where do you get that?` Look at the pictures. I fluctuate in weight a lot. And as far as my face, I`ve never had anything done."
The 26-year-old beauty has also revealed her spin-off MTV reality show `Audrina` won`t be returning for a second series.
The brunette star - who has also competed on `Dancing with the Stars` - said: "I don`t think we are. We finished in April and I kind of decided I wanted to take some time off from reality. I want to do something more like acting or hosting."