Ever wondered how some celebrities seem to defy the aging process? The secret is not always good genes or the most expensive skincare products that money can buy. Sometimes, it takes a contribution from cosmetic surgeons who are willing to help with a little nip, tuck, or wrinkle-smoothing injection.While Courteney Cox called getting fillers the "biggest beauty regret" of her life, Sharon Osbourne said she has done so much facial surgery that there isn't "that much skin left to stretch, pull, cut."From Megan Fox to the Kardashian siblings, here are some stars that have altered their appearance with plastic surgery.