The 'Snow White and the Hunstman' star has looked up to many people in Hollywood who turned out to be "fake" when she met them.
Talking about beauty, she said: "If you don't have the heart to back up your looks, you are ugly.
"I've met so many people that I thought were so gorgeous and talented and amazing. And then you meet them for one second and you're like ... you are wearing a costume, you are a fake, you are so unattractive."
"And it doesn't always come across in a picture, but you can be really beautiful in a still frame, and then, in life, moving around, you're ugly."
The 22-year-old actress describes herself as particularly "intense," but admits her fun side does occasionally surface too.
Kristen - who is dating her 'Twilight Saga' co-star - told The Guardian newspaper: "Yeah, I'm still a very intense person.
"I'm chilled out about some things. I'm cool. But definitely, I take things far too seriously. I am just a serious person. I love joking around, and it's obviously about mood, because sometimes I can definitely be a silly idiot.
"But most of the time I am like [private]. And I'm overtly aware of f***ing everything [up]."