Demi Lovato says she was bullied mercilessly in middle school, which helps explain why she's thrilled to be the new ambassador for Secret's "Mean Stinks" campaign.

"I heard about the program last year, and thought it was such a great opportunity," the 'X Factor' judge tells People. "They're really trying to put an end to bullying."

The campaign urges teen girls to wear blue nail polish on their pinky fingers as a sign that they won't participate in or tolerate bullying. Lovato plans to sport the nail polish herself. "I'll definitely be wearing it starting soon," she promises. "It's a conversation starter: 'Hey, why is your pinky blue?' 'This is a pinky promise that I'm not going to bully people, that me and my friends are ganging up for good.'"

With a mentor slot on a hit tv show and a successful album, Lovato is flying high at the moment, but the 20-year-old isn't that far removed from her own struggles with being taunted and teased. "I had a really tough time when I was in middle school," she says. "People would write 'hate petitions' [about me] and send them around to be signed. They'd have CD-bashing parties of my demos. They'd come to my house, stand across the street and yell things. It was a very emotional time for me, and all I wanted to do was get away."

Lovato's issues with self-esteem were part of the reason she checked into a facility to seek treatment in 2010, but now she is proud to be in a position to be able to give back to others. Secret has pledged to donate $1 from every Mean Stinks Clinical Strength deodorant to support the campaign.

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