Why Mary Kate Olsen won't smile

You see a tabloid shot of Mary-Kate Olsen and think, "Why does she look so depressed?" Well, there's a reason for that.

"I don't want my picture taken," the 21-year-old actress tells Entertainment Weekly magazine. "The only time I think it's OK is at a red-carpet event or a photo shoot.

"So every time I see paparazzi, I cover my face so they don't get a picture, and I'm just 'the mean person who doesn't smile.' "

Olsen, whose waiflike figure has made her a target of media scrutiny, avoids public displays of attention.

"I would love to be able to swim in the ocean in Malibu," she says. "But that is asking for a bikini shot. That's inviting something that I don't want to happen. I don't need to be on a 'Who's Skinny, Who's Fat, Who's Looking Healthy, Who's Not Eating?' list."

After a hiatus from acting, Olsen -- who rose to fame on TV's "Full House" in a shared role with twin sister Ashley -- will portray an alluring Christian girl on Showtime's "Weeds." Her 10-episode arc begins September 17.

She also returns to the big screen in "The Wackness," co-starring Ben Kingsley. The film is slated for release next year.