For many years, physicians thought that stressful lifestyles and diets containing spicy foods contributed to the corrosion that causes peptic ulcers. In the 1980s, physicians identified the Helicobacter pylori (H. pylori) bacterium, which has since been associated with most peptic ulcers. H. pylori infection causes almost two-thirds of all peptic ulcers, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Unlike most bacteria, H. pylori are able to survive and even thrive in the highly acidic gastric (stomach) environment. They grow in the mucous barrier that protects the gastrointestinal (GI) lining from the digestive juices. H. pylori bacteria also produce large amounts of urease, an enzyme that breaks down to form ammonia. Ammonia neutralizes the acidity around the bacteria, further protecting them.

H. pylori interferes with the mucosal defenses against the digestive juices, as well as producing its own toxins. Further, chronic infections cause the overproduction of stomach acid, which may irritate and break down the weakened stomach lining. H. pylori infection also causes gastritis, an irritation of the GI lining, which sometimes develops before a peptic ulcer.

Any contact that transports H. pylori bacteria to the stomach may produce H. pylori infection. However, the mechanisms of H. pylori action on the GI lining are not well understood. Many people harbor the H. pylori bacteria, but not all of them develop peptic ulcers or gastritis. H. pylori can be passed through food, water or close contact with a person who has the bacteria. In addition to the stomach, H. pylori bacteria have been found in saliva and feces.

Nearly two-thirds of the world’s population carries the H. pylori bacteria, according to the U.S. Centers for Disease Control and Prevention. In the United States, the bacteria occur more commonly in older adults, African Americans and Hispanics.

Nearly all peptic ulcers that are not caused by H. pylori bacteria result from the use of certain medications. Many medications may irritate the GI lining and cause peptic ulcers. Certain pain relievers called nonsteroidal anti-inflammatory drugs (NSAIDs) are most likely to do so, especially with chronic use. These commonly used pain relievers (including aspirin and ibuprofen) reduce the action of prostaglandins, one of the components of the mucous barrier in the stomach. Other medications, including corticosteroids, may also lead to the formation of peptic ulcers. However, not all people taking these medications develop ulcers.

Almost all cases of peptic ulcers are caused by either H. pylori bacteria or the use of anti-inflammatory medications. A few cases may be attributed to other causes such as severe stress resulting from significant illness or injury (e.g., kidney failure, severe burns, peritonitis). Such stress may cause decreased blood flow to the organ lining and impair the healing ability of the mucous barrier. Although rare, cancerous tumors in the stomach or pancreas may also cause peptic ulcers.

In addition to the known causes of peptic ulcers, certain risk factors have been identified for their development. These include:

• Family history of peptic ulcers. Heredity may predispose a patient to peptic ulcer formation.
  
  
• Age. The risk of peptic ulcers increases with age. The ability of the stomach lining to resist damage decreases with age. In addition, older people are more likely to harbor the H. pylori bacteria and take more NSAIDs for medical conditions.
  
  
• Personal differences in stomach acid production. Some people normally produce a lot of stomach acid and some produce much less. Those who produce more have a greater risk of peptic ulcers.
  
  
• Substance abuse. Excessive alcohol consumption, cigarette smoking or illicit drug use can weaken the stomach lining’s defenses against digestive acids. Smoking also makes ulcers heal much more slowly.
  
  
• Diet. Although diet does not directly cause peptic ulcers, it may increase the risk of developing them and make them worse. Many foods (especially those that are spicy, acidic, fried or fatty) may irritate the stomach lining.
  
  
• Stress. Even minor stresses can increase the production of stomach acids and slow digestion, increasing the risk of peptic ulcers and making existing ulcers worse.