It's no accident that when stars play unattractive on screen — Kate Winslet in "The Reader," Kidman in "The Hours," Charlize Theron in "Monster" — they crank up the femme fatale factor on the red carpet.

"Hilary Swank didn't show off her figure in 'Boys Don't Cry,'" says Tanya Gill, her stylist of three years. "But when she went to the Globes, it was in a sheer Versace couture dress. The year of 'Million Dollar Baby,' you saw more of her body. She wasn't going to hide how much she worked for those parts."

Then there's the "suddenly single" moment. Reese Witherspoon donned a succession of princess styles before her breakup with Ryan Phillippe. But when she emerged in 2007 in a short, tight, strapless yellow Nina Ricci, the message was: "He's gone, but I'm still sexy! And available!"

"Actresses have to walk a tightrope," says Cameron Silver, owner of vintage boutique Decades, from where many Globes gowns hail. "Too avant-garde and you're a 'fashion girl.' Too underdone and you're on the worst-dressed list. You want that middle space occupied by Penelope Cruz or Jennifer Garner: serious actress who happens to be chic."

In the case of certain actresses — think Camilla Belle or Diane Kruger — they're much better known for outfits than for acting. "It's not so bad being famous for style, if you want to be famous," Stewart says. "It's not their fault they look good in clothes."

So do Cate Blanchett and Tilda Swinton, but they work constantly.

"When an actress dresses authentic to who she is, she can go as far as she likes," Stewart says. "That demands true talent."

But when the scales tip and it's all style over substance, one stylist admits, "you wind up with free clothes and no parts."

Adds the major talent manager of one fashionista: "If there's too much emphasis on fashion, you do get taken less seriously as an actress. Courting the balance these days is almost harder than getting a great part — statuesque doesn't always lead to a statue."