The X-Factor judge said her main objection is that people start to look the same instead of valuing their individuality.
She told the News of the World: "There is a massive difference between here [the UK] and LA. In Hollywood you see surgery all the time, walking down the street. But I don't think it's good or nice, because everyone looks the same. Part of being you is your uniqueness and identity. If you get the same surgery as the woman next door then chances are you'll start looking the same. That's just not good. [But] we have a responsibility to feed women a positive body image. And judging people on their decisions - be it body weight or the surgery they've had - is a bad message."
The 27-year-old added she will be staying away from Botox, unlike fellow judges Simon Cowell and Dannii Minogue.