What causes stomach ulcers

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Last updated: April 4, 2026

Quick Answer: The primary causes of stomach ulcers are infection with the bacterium Helicobacter pylori (H. pylori) and the long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). Less commonly, Zollinger-Ellison syndrome, a rare disorder causing the stomach to produce too much acid, can also lead to ulcer formation.

Key Facts

H. pylori bacteria infects the stomach lining in about half of the world's population.
NSAIDs like ibuprofen and naproxen account for a significant percentage of ulcer cases.
Stomach acid is a major factor in ulcer development, eroding the protective lining.
The prevalence of H. pylori-related ulcers has decreased in some developed countries due to better hygiene and antibiotic treatments.
Smoking and excessive alcohol consumption can worsen ulcer symptoms and hinder healing.

Overview

Stomach ulcers, also known as peptic ulcers, are open sores that develop on the inside lining of your stomach and the upper portion of your small intestine (duodenum). While often referred to as stomach ulcers, they can occur in either location. The digestive system is lined with a protective mucus layer that normally prevents the stomach's potent digestive acids from damaging the stomach wall. When this protective layer is compromised, or when acid production increases significantly, the stomach lining can become inflamed and eroded, leading to the formation of an ulcer.

Common Causes of Stomach Ulcers

1. Helicobacter pylori (H. pylori) Infection

The most common culprit behind stomach ulcers is infection with a bacterium called Helicobacter pylori (H. pylori). This bacterium is incredibly common, infecting the stomach lining of approximately 50% of the world's population. While many people infected with H. pylori never develop symptoms or ulcers, the bacteria can inflame the stomach lining (gastritis) and disrupt the protective mucus layer. This disruption allows stomach acid to reach and damage the underlying tissue, causing an ulcer. H. pylori is thought to be spread through contaminated food or water, or through close contact with an infected person's saliva or vomit. Poor sanitation and crowded living conditions are associated with higher rates of infection.

2. Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

Another major cause of stomach ulcers is the frequent or long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs). These medications are widely available over-the-counter and by prescription to relieve pain, reduce fever, and decrease inflammation. Common examples include ibuprofen (Advil, Motrin), naproxen sodium (Aleve), and aspirin. NSAIDs work by blocking enzymes called COX-1 and COX-2, which are involved in producing prostaglandins. Prostaglandins play a crucial role in protecting the stomach lining by increasing mucus production and blood flow. When NSAIDs inhibit these prostaglandins, the stomach's defense mechanism is weakened, making it more susceptible to acid damage and ulcer formation. The risk of developing an ulcer from NSAIDs increases with higher doses, longer duration of use, and in older adults.

Less Common Causes

3. Zollinger-Ellison Syndrome

Zollinger-Ellison syndrome is a rare disorder that causes one or more tumors, called gastrinomas, to develop in the pancreas or duodenum. These tumors produce excessive amounts of a hormone called gastrin. Gastrin stimulates the cells in the stomach lining to secrete large quantities of gastric acid. This overproduction of acid can overwhelm the stomach's protective mechanisms, leading to severe and often multiple peptic ulcers. This condition is responsible for less than 1% of all peptic ulcers.

4. Other Contributing Factors

While H. pylori and NSAIDs are the primary causes, other factors can increase your risk of developing ulcers or worsen existing ones:

Smoking: Smoking can increase stomach acid production, reduce blood flow to the stomach lining, and impair the healing process of ulcers.
Excessive Alcohol Consumption: Alcohol can irritate and erode the stomach lining, making it more vulnerable to damage from digestive acids.
Severe Stress: While not a direct cause, severe physical stress from major surgery, burns, or serious illness can contribute to ulcer development or delay healing. Psychological stress alone is not considered a direct cause of ulcers, but it can exacerbate symptoms.
Certain Medical Conditions: Conditions like Crohn's disease or sarcoidosis can sometimes lead to ulcers.
Certain Medications: Besides NSAIDs, other medications like corticosteroids, when used long-term, may increase the risk of ulcers.

Mechanism of Ulcer Formation

The formation of a stomach ulcer is essentially an imbalance between the aggressive factors (acid, pepsin, H. pylori) and the protective factors (mucus, bicarbonate, blood flow, prostaglandins) of the stomach lining. When aggressive factors dominate, the lining is damaged. H. pylori contributes by producing enzymes that damage the mucus layer and by triggering inflammation that further weakens the defenses. NSAIDs directly impair the production of protective prostaglandins. The resulting erosion creates an open sore that can bleed, cause pain, and, if left untreated, lead to serious complications.