Peptic ulcers are sores shaped like craters, and they develop when the digestive juices produced by the stomach erode or eat away the lining of the digestive tract. Peptic ulcers may form in the lining of the stomach (gastric ulcers) or just below the stomach, at the start of the small intestine (duodenal ulcers).

The most common causes of peptic ulcers are infection with Helicobacter pylori (H. pylori) bacteria and frequent use of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs).