Ulcers are painful, open sores that develop on the lining of the stomach, small intestine and esophagus. They are caused by a bacteria called Helicobacter pylori. Ulcers that do not heal with treatment may indicate a resistant form of H. pylori or other factors interfering with the healing process like smoking, alcohol or NSAID use, and sometimes/rarely caused by extreme overproduction of stomach acid, stomach cancer, or Crohn's disease.
