There is no clear evidence to suggest that the stress of modern life or a steady diet of fast food causes ulcers in the stomach and small intestine, but they are nonetheless common in our society: About one out of every 10 Americans will suffer from the burning, gnawing abdominal pain of a peptic (or gastric) ulcer sometime in life.

Peptic ulcers are holes or breaks in the protective lining of the duodenum (the upper part of the small intestine) or the stomach — areas that come into contact with stomach acids and enzymes. Duodenal ulcers are more common than stomach ulcers. Comparatively rare are esophageal ulcers, which form in the esophagus or swallowing tube and are often a result of alcohol abuse. While excessive stomach acid secretion certainly plays a role in the development of ulcers, a relatively recent theory holds that bacterial infection is the primary cause of peptic ulcers.

Other factors also seem to contribute to ulcer formation. Overzealous use of over-the-counter painkillers (such as aspirin, ibuprofen, and naproxen), heavy alcohol use, and smoking exacerbate and may promote the development of ulcers. Research indicates that heavy smokers are more prone to developing duodenal ulcers than are nonsmokers, that people who drink alcohol are more susceptible to esophageal ulcers, and that those who take aspirin frequently for a long period of time are more likely to develop stomach ulcers than those who don’t.

Duodenal ulcers tend to appear in people with type O blood, possibly because they do not produce the substance on the surface of blood cells (hence type O) that may protect the lining of the duodenum.