Just like the internal lining of the mouth can break open to form a painful sore the stomach lining can also get affected and develop an ulcer called gastric ulcer or peptic ulcer. But ulcers in the stomach are more serious and may require hospitalisation in serious cases. What causes peptic ulcers? The most important function of your stomach is to digest the food you eat with the help of acids and a substance called pepsin produced by the cells lining of the stomach. Unfortunately these acids along with pepsin are strong enough to attack your stomach and duodenal lining.