Gastritis is an inflammation of the lining of the stomach. There are several forms, including chronic gastritis (symptoms are usually indefinite or nonexistent) and acute erosive gastritis (symptoms may include vomiting, vomiting blood, black, tarry feces, anorexia nervosa, and nausea).

In the 1990s, scientists discovered that the main cause of chronic gastritis is infection from a bacterium called Helicobacter pylori (H. pylori). This micro-organism has an outer layer that is resistant to the normal effects of stomach acid in breaking down bacteria, so it may rest in the stomach for long periods, even years, causing symptoms of gastritis or ulcers when other factors are introduced, such as the presence of specific genes or ingestion of nonsteroidal anti-inflammatory drugs (NSAIDS). Study of the role of H. pylori in gastritis and peptic ulcers has disproved the former belief that stress led to most stomach and duodenal ulcers. H. pylori is...