Given the fact that Sara Jean Underwood is a former Playmate, it's likely she had plastic surgery at some point. She's thought to have had a nose job and breast implants. In this first before and after pic we can see a very subtle difference in the shape of her nose. It's also possible that she had the rhinoplasty before any of these photos. She has a slight dent in the bridge of her nose that doesn't seem like it could be there naturally.
* 19000 Page Views