Kristen Stewart thinks she needs a "face transplant" to look happier when she meets fans.

The 'Twilight Saga' actress - who admits she finds fame difficult and is often criticised for looking sullen in public - tries hard to "smile" and look happy when she's approached by strangers, but can never relax fully.

She said: "I totally am more comfortable now. I try not to have that thing that people have which is like a celebrity skin and I think that's maybe where I run into problems.

"I have had so many people say, 'Why don't you just play the part? Just like, go smile, talk about whatever they want you to talk about.' It's like, 'I do, I really try to do that.' I guess I should get a face transplant or something. But it's gotten weird. I've like, relinquished control."

Despite trying hard to relax, the 20-year-old star doesn't plan to alter her persona for others.

She explained to US TV show 'Access Hollywood': "People are much better at doing this than I am and that's fine and I'm getting better and whatever, but I'm not gonna try to force myself to do anything."

Since her rise to fame as Bella Swan in the vampire franchise, Kristen has kept relatively quiet about her personal life, including rumours she is dating her co-star Robert Pattinson.

The 'Runaways' actress deliberately avoids social networking websites like twitter, which are often updated with reports on her whereabouts.

She added: "I'm not a huge fan. I just wouldn't have one.

"I'm gonna start walking around with a squirt gun. And just be like, 'No, it's cool.' I'm not trying, I mean, just to. like squirt their phones. Yeah, twitter's kind of crazy."