The urothelium is a unique lining in the body providing a protective barrier against the penetration of toxic agents, urine, and bacteria. The glycosaminoglycan (GAG) layer consists of a thick mucus layer of glycoproteins and proteoglycans on the surface of the urothelial cells. Damage to the GAG layer disrupts its protective barrier function giving rise to increased permeability into the deep layers of the urothelium and bladder, causing inflammation and pain. Replenishment of the GAG layer appears to restore normal permeability allowing for urothelial layer recovery.