Peptic ulcers are holes or breaks in the protective lining of the duodenum (the upper part of the small intestine) or the stomach -- areas that come into contact with stomach acids and enzymes. Duodenal ulcers are more common than stomach ulcers. Comparatively rare are esophageal ulcers, which form in the esophagus -- or swallowing tube -- and are often a result of exposure to medications, like certain antibiotics or anti-inflammatories, or alcohol abuse.