Which bacterium causes most peptic ulcers?

The bacterium that causes most peptic ulcers is Helicobacter pylori. This spiral-shaped bacterium can colonize the stomach’s protective lining, where it causes long-lasting inflammation and weakens defenses against stomach acid.

H. pylori survives in the acidic stomach partly by producing urease, an enzyme that helps create a less acidic local environment. It attaches to stomach-lining cells and can trigger inflammation, disrupting the balance between protective mucus, tissue repair, and digestive acid. Infection is also associated with gastritis and an increased risk of certain stomach cancers.

For much of the 20th century, ulcers were commonly blamed on stress, spicy food, or excess acid alone. Australian researchers Robin Warren and Barry Marshall identified the importance of H. pylori in the early 1980s. Their work changed treatment from mainly acid relief to antibiotic-based eradication therapy, and they received the 2005 Nobel Prize in Physiology or Medicine.

H. pylori is not the only cause of peptic ulcers. Long-term or heavy use of nonsteroidal anti-inflammatory drugs, such as ibuprofen or aspirin, is another major cause. Doctors generally test for the infection and use combinations of antibiotics plus acid-suppressing medicine when it is present.