Ulcers are caused by stress and spicy food

What actually happened

This is the flagship example of medicine being confidently, expensively wrong. The stomach was assumed sterile, because nothing could live in hydrochloric acid, so a bacterial cause was not merely unproven but considered absurd. An entire industry of antacids and a whole psychosomatic literature rested on it.

Warren saw the bacteria in biopsy samples in 1979. Marshall, a young registrar, took the idea seriously and could not get it published or funded. In 1984, unable to run the experiment any other way, he drank a broth of the organism himself, developed gastritis within days, and demonstrated it by endoscopy. The NIH Consensus Development Conference in February 1994 endorsed antibiotic treatment, and that is the fair date for the mainstream turning.

The consequences were large. A chronic, recurring, sometimes fatal disease became a two-week cure. H. pylori is also a Group 1 carcinogen and a major cause of gastric cancer, so eradicating it prevents cancer too. The honest refinement: stress and diet are not entirely irrelevant, since they can worsen symptoms, and roughly a fifth of ulcers have other causes. But the core mechanism taught in schools for decades was simply wrong, and the people who found the truth were mocked for a decade first.