An ulcer is an open sore on the surface of an organ or tissue. Ulcers most commonly erupt in the esophagus, stomach, and duodenum, in which case they are known as peptic ulcers. Peptic ulcers —sores in the lining of the stomach or intestines—can largely be blamed on a bacterium called Helicobacter pylori (H. pylori), a spiral-shaped micro-organism that can live...