Katherine Heigl has a makeup secret: she loves beauty products!

"When I was in Rhode Island filming (27 Dresses) this summer, I went to Sephora for the first time," she tells InStyle. "It was a holy mecca."

Turns out, her initiation into the cosmetics world brought about a transformation in her bathroom, which she has reorganized to accommodate her treasure trove of products - some of which she gets for free.

"I love getting those boxes," she says.

And while the Grey's Anatomy star and Emmy winner, 28, admits that her arms are wide open to freebies, she does have her limits.

"There comes a point of gluttony I can't accept," she says. "When that happens, I feel like I have to clean out and give stuff to my sister, mom and friends."

While Katherine Heigl admits to being conscious of her looks to the point of her always wearing full makeup in public - "I do not want to be the 'Look What This Celebrity Looks Like Without Makeup' picture," she says - she is also candid about what she considers her imperfect attributes: her complexion and teeth.

"My skin is sensitive, so everything bothers it," she says. "And I'm the jerk who keeps switching products and making it worse."

Heigl also wears an Invisalign retainer, which she removes during the InStyle interview before eating. "I got them because of this wonky tooth," she says. "It's awesome because every two weeks you switch to a new retainer. Pretty much the perfect way to describe Invisalign is Netflix for your teeth."

For her InStyle Hollywood Hair Makeover shoot, the self-professed product fanatic got to try on three different looks for three different covers.

Posing with a glamorous updo, a short, brunette wig and her hair in loose ringlets, Katherine Heigl raved about the experience.

"To have these professionals turning you into someone else is pretty neat," she says â€" especially when it came to her hair. "I've always wanted to be a brunette because in a town of blondes, it makes me look a little more exotic," she says.

Still, she has a favorite look of the three: "The Ingenue," which she calls "sexy but not overtly so." The image, with her hair down and loose, seems to sum up Heigl's style perspective. Says Katie: "I like simple hair and makeup."

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.