For most of the twentieth century, peptic ulcers were understood as a disease of lifestyle. Stress, alcohol, and spicy food were considered the main culprits. The standard treatment was antacids, milk, and bland diets. The relief was temporary, and ulcers usually returned.

In 1982, two researchers in Western Australia — the gastroenterologist Robin Warren and his junior colleague Barry Marshall — examined biopsies from the stomachs of ulcer patients. They observed a curved, spiral-shaped bacterium living in the tissue. They proposed that this organism, later named Helicobacter pylori, was the actual cause of most peptic ulcers and a major risk factor for stomach cancer.

The medical establishment did not believe them. The standard view was that the human stomach, with a pH around 1.5, was too acidic to support bacterial life. Marshall's grant applications were rejected. Major journals declined his early papers.

In 1984, Marshall conducted an unauthorized experiment on himself. He prepared a broth containing roughly a billion H. pylori organisms cultured from a patient and drank it. Within a week he developed acute gastritis — inflammation of the stomach lining — along with severe nausea. A biopsy confirmed the bacterium had colonized his gut and inflamed the tissue. He treated himself with a course of antibiotics and recovered.

The self-experiment was the turning point. Within a decade, clinical practice shifted. Peptic ulcers, which had been a chronic and recurring condition for millions of people, were reclassified as an infection. Today they are routinely cured with a short course of antibiotics combined with acid suppression. The cure rate is over 90 percent.

In 2005, Marshall and Warren shared the Nobel Prize in Physiology or Medicine.