Stomach ulcers, also known as peptic ulcers, are open sores that develop on the lining of the stomach or the upper part of the small intestine. They occur when stomach acid erodes the protective lining, leading to symptoms such as burning stomach pain, indigestion, nausea, and in severe cases, bleeding. Common causes include infection with Helicobacter pylori (H. pylori) bacteria, long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs), and excessive alcohol consumption. Treatment typically involves medications to reduce stomach acid, antibiotics to treat H. pylori infection, and lifestyle changes to promote healing.