A peptic ulcer is a sore that develops on the lining of the stomach or the first part of the small intestine, known as the duodenum. These ulcers occur when the protective mucus layer is reduced, allowing stomach acid to damage the tissue. Common causes include infection with Helicobacter pylori bacteria and the long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). Symptoms of a peptic ulcer may include burning stomach pain, bloating, and indigestion. If left untreated, ulcers can lead to serious complications, such as bleeding or perforation of the stomach wall. Treatment often involves medications to reduce stomach acid and antibiotics to eliminate H. pylori infection.