Gucci gal Blake Lively knows its time to hit the gym when....

LOS ANGELES – She is routinely considered one of the most beautiful women in the world, and the object of desire in roles from CW’s “Gossip Girl” to Oliver Stone’s “Savages,” but Gucci’s latest glam girl, Blake Lively, still suffers from insecurities most people can relate to.

“When I gain weight, I can always tell when I try to put my jeans on,” she told FOX411’s Pop Tarts column. “I tend to gain weight in my hips, so when I know my jeans are a little tight it’s ‘oh crap, time to work it off.’”

And being in an industry centered on physical appearance, Lively, 25, has had to learn ways to put hers into perspective.

“You have to not put your worth in other people. If you put yourself in front of a crowd of people, you will never get a unanimous vote if they love your outfit or they hate it, if they love the way you look or they don’t,” she explained. “You have to really play to yourself. People always ask me what my biggest red carpet regret is, but I don’t look back on those outfits with regret. I just think I wouldn’t wear it not because my style has evolved – you can’t let other people judge or determine your self-worth.”

Yet even with paparazzi lurking at every turn, don’t expect this former “Gossip Girl” star to be snapped sauntering the streets in sweat pants.

“I love dressing up. I’ll walk around with no makeup on, with my face broken out or my hair a disaster but I will still dress up in great heels or a beautiful bag, because that’s just what I do,” Lively said. “I feel bad about myself when I am wearing the same pajamas at dinner that I woke up in because I think, ‘I really bummed it in today, why didn’t I care more about myself?’ But if that makes you feel more confident and relaxed, then do that. For me, I love dressing up. I wear gowns around my house because I go in my closet and am like, ‘Ohhh I love this dress so much!’ and I just want to wear it. I guess I am like a little girl at a tea party.”

And clearly her passion for fashion impressed the powers-to-be at iconic brand Gucci as the Southern California native and wife of Ryan Reynolds was recently named the first face of Gucci’s Première, the company’s signature female fragrance.

“It is an empowered looking woman, never a meek woman. She is very strong and very sunny and glowing. To be asked to be a part of that is truly humbling,” Lively said. “And I really love that the fragrance represents women very well, that it has the citrus which is sassy and the wood which is very masculine, it really encompasses a story in itself.”

Danielle Jones-Wesley contributed to this report.