A stomach ulcer, also known as a gastric ulcer, is a sore that develops on the lining of the stomach. It occurs when the protective mucus layer is weakened, allowing stomach acid to damage the tissue. Common causes include infection with Helicobacter pylori bacteria, long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs), and excessive alcohol consumption. Symptoms of a stomach ulcer may include burning stomach pain, bloating, and nausea. 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.