Stomach ulcer. Gastroscope (endoscope) view of a gastric (peptic) ulcer of a 82 year-old female patient. This ulcer (upper centre, red) was revealed after a clot (lower centre, purple) had been washed (lavaged) away. Ulcers are caused by excessive stomach acid (digestive juice). This acid, often combined with excess alcohol and caffeine, attacks the stomach wall, causing pain and discomfort. If the wall's protective mucus becomes thinned, possibly due to mental stress or bacterial attack, the acid can perforate the stomach wall. A perforated ulcer can result in anaemia and vomiting blood (haematemesis).