Bane wears a mask because it dispenses an anesthetic gas that helps control and relieve the chronic pain he suffers from serious injuries sustained previously. The mask is essential for keeping his pain at a tolerable level, allowing him to function and maintain his physical strength and fighting ability. In Christopher Nolan's film The Dark Knight Rises, this explanation makes Bane even more formidable, as the mask allows him to endure and operate despite his debilitating pain. Without the mask, Bane becomes powerless and vulnerable.
