Credit: Mario Testino/Vogue

Jessica Biel hates getting glammed up.

"When I see myself in pictures with makeup on, even to this day, I think it looks weird," Biel, 27, admits in the February issue of Vogue. "My eyes get squintier and smaller."

The Valentine's Day star -- who recently climbed Mt. Kilimanjaro -- says she's "playing a character" every time she's photographed on the red carpet.

"As soon as I get off that thing I think, 'Oof, wipe that gloss off,'" she admits. "I’m wiping and wiping and pulling my hair out and trying to change my outfit. I’m immediately trying to get comfortable. It’s really a part I play."

Not that on-again beau Justin Timberlake (whom she began dating in 2007) minds her dressed down.

See photos of all the women who have been linked to Justin Timberlake

"Pretty is cool, but it's not really about looks for me," he once said. "It's more about personality. I like a girl with a good sense of humor, who's humble and sensitive."