Ulcers and the Bacteria That Causes Them

Ulcers were believed to be caused by stress, smoking, anxiety, and/or a diet rich in spicy foods. However, research has shown that most ulcers are caused by a spiral-shaped bacterium known as Helicobacter pylori (H. pylori). The other common cause of ulcers is nonsteroidal anti-inflammatory drugs (NSAIDs).

Anatomy of an Ulcer

When we eat, food passes down the esophagus (throat) and into the stomach. There, hydrochloric acid and pepsin (an enzyme) continue the digestive process that started with the saliva in your mouth. Next, food passes to the duodenum (small intestine) where the digestive process continues. An ulcer is an area of stomach or duodenum that has been damaged by the digestive enzymes and stomach acid.

How H. pylori causes ulcers is not yet fully understood. We do know that:

  • The bacteria can live in the stomach because they attach to cells and produce an enzyme that stops the corrosive effects of stomach acid.
  • The bacteria damages the protective mucous layers of both the stomach and the duodenum.
  • Not everyone who has the bacteria will develop an ulcer.
  • Being infected with the bacteria is also a risk factor for developing stomach cancer.

An ulcer that goes untreated can cause several problems in the abdomen, such as:

  • Internal bleeding
  • Perforation (a hole) in the stomach or duodenum allowing food and bacteria to spill into the abdomen and cause infection and irritation
  • Blockage of the opening between the stomach and duodenum due to chronic inflammation that leads to swelling and scarring

Discovering the Causes of Ulcers

The story behind the discovery of the H. pylori bacteria and its relationship to ulcers is an unusual one. In 1982, two Australian researchers, Drs. Barry Marshall and Robin Warren, detected the bacteria in the stomach lining of people suffering from gastritis. When further study demonstrated the presence of the bacteria in nearly 100% of patients with duodenal ulcers and 80% of people with stomach ulcers, Drs. Marshall and Warren proposed that it might be the cause.

When their hypothesis was met with a great deal of skepticism, Dr. Marshall ingested a teaspoonful of the bacteria. Within 24 hours, he developed severe gastritis. Further research by Dr. Marshall, Dr. Warren, and others established that it does in fact cause 50% of stomach ulcers and 90% of the much more common duodenal ulcers.

Of the ulcers that are not caused by H. pylori, most are caused by NSAIDs (nonsteroidal anti-inflammatory drugs), such as ibuprofen, and naproxen. NSAIDs block the production of mucous in the stomach that protects the lining from the damaging effects of the stomach acid.

The Telltale Burn

The most common symptom of an ulcer is a chronic burning pain in the upper part of the abdomen. The pain is usually between the breastbone and the naval and it can last from minutes to hours. Pain often occurs in the middle of the night, upon waking, and/or 2-3 hours after a meal. It may be relieved by eating or taking antacid medicines. Less common symptoms include:

  • Nausea
  • Vomiting—can be bloody or appear like coffee grounds if the ulcer is bleeding
  • Loss of appetite
  • Loss of weight
  • Bloody or black stool caused by bleeding from the ulcer
  • Weakness


It is important that ulcers be properly diagnosed. The symptoms common to ulcers can also be caused by a number of other conditions. In addition, ulcers caused by H. pylori and those caused by NSAID are treated somewhat differently.

The 2 most commonly used tests for diagnosing an ulcer are:

  • Endoscopy—an examination of the esophagus, stomach, and duodenum using a small, flexible tube-like instrument containing a camera that is inserted through your throat
  • Upper GI series—x-rays of the esophagus, stomach, and duodenum are taken after you drink a chalky substance that outlines the shape of the digestive tract

A test for the presence of H. pylori is done to determine whether the ulcer is caused by the bacteria. There are several methods used to detect it including a blood test, a breath test, or a lab analysis of the biopsied tissue sample. These tests differ in sensitivity for detecting the presence of bacteria in your system.

Removing the Offending Agent

Treatment involves removing the underlying cause of the ulcer and healing the ulcer. One common treatment approach involves taking antibiotics to eliminate the bacteria along with an acid suppressor and sometimes a bismuth-containing medication such as Pepto-Bismol. This method is often effective in killing the bacteria, healing the ulcer, and preventing it from returning.

Steering Clear of Ulcers

To prevent NSAID-caused ulcers, try to avoid using NSAIDs in large doses for long periods of time. Unfortunately, researchers do not yet know how to prevent the development of H. pylori in the digestive tract. Some recommended precautions are to:

  • Wash your hands thoroughly after using the bathroom and before eating.
  • Eat food that has been washed and cooked.
  • Drink water from a clean source.


The American College of Gastroenterology
National Institute of Diabetes and Digestive and Kidney Diseases


College of Family Physicians of Canada


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Last reviewed January 2016 by Michael Woods, MD
Last Updated: 3/10/2014

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