Why Zebras Don't Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Diseases, and Coping

by Robert M. Sapolsky

up to 15 percent of duodenal ulcers form in people who aren’t infected with Helicobacter, or with any other known bacterium related to it. More damning, only about 10 percent of the people infected with the bacteria get ulcers.