Ulcers result from three main causes: infection with Helicobacter pylori , use of nonsteroidal anti-inflammatory drugs (NSAIDS), and pathologic hypersecretion of gastric acids.

Ulcers may occur anywhere in the esophagus, stomach, pylorus, duodenum, or jejunum, with the crater of the ulcer penetrating through one or more layers of tissue. If this damage is recurring or if healing doesn't take place, the crater may penetrate the wall and extend to adjacent tissues and organs, such as the pancreas.

The bacteria Helicobacter pylori are a contributing factor in chronic gastritis (chronic inflammation of stomach mucosa) and in ulcer formation. They're typically seen within the muscular layers and between cells that line the gastric pits. These bacteria cause tissue inflammation, which can lead to ulcers.

In the absence of an effective mucous barrier, an irritant can cause the basal lamina to exfoliate or slough off. A process called rapid reepithelialization, shown below, replenishes the damaged epithelium and repairs any defects.