Board Thread:Theories and Speculation/@comment-3568954-20141031085827/@comment-10330822-20141109015137

Sakura explained that Tsunade uses the power of the seal to stimulate her special transformation jutsu. You're right that it isn't the seal, but if the seal would disappear, the jutsu that transforms her would end right after that. Hence, why she always turns old after losing her Reverse Seal. Sakura explained she can use more of the seal's power because she doesn't have to use it to keep up her appearance.