Peptic ulcers are believed to develop because of increased acid and pepsin secretion, a reduced mucosal defense mechanism, or a combination of these two abnormalities. Environmental factors such as use of nonsteroidal and steroidal anti-inflammatory drugs, smoking, and emotional stress may play a role in the pathogenesis of ulcer disease in some patients. The exact mechanisms whereby these factors cause ulcers is unknown, although it is likely that non-steroidal drugs cause ulcers by reducing mucosal defense mechanisms whereas emotional stress may lead to ulceration by increasing acid secretion and/or decreasing mucosal defense mechanisms. Genetic factors may be important in the pathogenesis of ulcers in some patients.