For decades, doctors thought that genetics or anxiety or even spicy foods caused stomach ulcers. Scientists now believe that stress and spicy foods only worsen the pain of an ulcer. The gastric ulcer itself is caused by a bacterium called Helicobacter pylori. Researcher Barry Marshall (1951–) of Australia observed that many ulcer patients had these bacteria present in their systems. In 1984, he designed an experiment to determine whether there was a link between Helicobacter pylori and stomach ulcers. He consumed a large amount of the bacteria. He developed ulcers ten days later. Ulcers are now treated with antibiotics. Marshall shared the 2005 Nobel Prize in Physiology or Medicine with J. Robin Warren (1937–) for their discovery of the bacterium Helicobacter pylori and its role in gastritis and peptic ulcer disease.