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Helicobacter pylori is the bacterium that causes more than half of peptic ulcers worldwide. The bacteria damages the mucous coating that protects the stomach and the duodenum. Damage to the mucous lining allows stomach acid to pass through the mucosal lining of the stomach and the duodenum.
However, most people with Helicobacter pylori develop ulcers and do not simply act as carriers. The mechanism by which the bacteria cause ulcers in some people but not in others is unknown. It is likely that the development of the ulcer depends on characteristics of the individual, the type of Helicobacter pylori strain, and the presence of other factors that are still unknown.
