In the underground tunnel scene where Bane and Batman fight, Bane has some odd texture covering the skin of his arms, mostly around the shoulders and upper arms. It almost looks like dry and cracked clay, or perhaps like fake skin that's peeling.
My best guess is that it's dirt or filth caked-on from the sewers. But it seems like such an odd and distracting prosthetic to add (IMHO), I wonder if there's more plot-like reason to it than meets the eye. I can't imagine Nolan would let a misapplied prosthetic slip by so noticeably, and at such a pivotal scene.
On the other hand, maybe it's intentionally supposed to add to the unsettling "grittiness" of the scene, like the harsh lighting of the scene (as explained in the extras).