Helicobacter pylori ("H. pylori") is a spiral shaped bacterium that lives in or on the lining of the stomach. It causes more than 90 percent of ulcers, which are sores in the lining of the stomach or the duodenum (the first part of the small intestine). Before 1982, when this bacterium was discovered, doctors thought that spicy food, acid, stress and lifestyle caused most ulcers. Because doctors now know that most ulcers are caused by an "H. pylori" infection, they can be cured with the correct antibiotics.