Causes of Ulcers Ulcers, particularly peptic ulcers, are sores that develop on the lining of the stomach, small intestine, or esophagus. The two most common types are gastric ulcers (in the stomach) and duodenal ulcers (in the first part of the small intestine). Here are the primary causes of ulcers: 1. Helicobacter pylori Infection 2.…