A peptic ulcer is an open sore that develops on the lining of the stomach (gastric ulcer), small intestine (duodenal ulcer), or esophagus. It results from an imbalance between digestive acids and the protective mucosal lining, often caused by Helicobacter pylori infection or long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). Symptoms include abdominal pain, bloating, heartburn, nausea, and sometimes bleeding. Diagnosis typically involves endoscopy. Treatment focuses on reducing acid, eradicating H. pylori, and protecting the mucosa.