what causes stomach ulcers
A bacterium. Helicobacter pylori bacteria commonly live in the mucous layer that covers and protects tissues that line the stomach and small intestine. Often, the H. pylori bacterium causes no problems, but it can cause inflammation of the stomach's inner layer, producing an ulcer. It's not clear how H. pylori infection spreads. It may be transmitted from person to person by close contact, such as kissing. People may also contract H. pylori through food and water.