Duodenal ulcers are open sores that form in the lining of the duodenum, the first section of your small intestine just beyond the stomach. The two most common causes are infection with a bacterium called H. pylori and regular use of common pain relievers like ibuprofen or aspirin. Together, these account for the vast majority of cases, though smoking, genetics, and rare hormone-producing tumors can also play a role.
To understand why ulcers form, it helps to know what normally keeps them from forming, and what happens when that protection breaks down.
How Your Duodenum Normally Protects Itself
Your stomach produces hydrochloric acid strong enough to break down food, and that acidic mixture passes directly into the duodenum. The duodenal lining survives this constant acid bath thanks to a layered defense system. A thick gel of mucus coats the surface, and cells beneath it secrete bicarbonate, a natural alkaline substance that neutralizes acid as it seeps into the mucus. This creates a pH gradient: the outer surface facing the stomach contents is highly acidic, but the tissue underneath sits at a near-neutral pH. The mucus layer also physically blocks pepsin, a digestive enzyme that would otherwise eat through the tissue.
When any of these defenses weaken, or when acid production overwhelms them, the lining erodes. That erosion is a duodenal ulcer.
H. pylori Infection
H. pylori is a spiral-shaped bacterium that colonizes the stomach lining, and it’s the single most common cause of duodenal ulcers worldwide. The bacterium anchors itself to the stomach’s surface cells using specialized adhesion proteins that latch onto molecules in the gastric mucus. Once attached, it triggers a chain of events that tips the balance between acid attack and mucosal defense.
H. pylori provokes a persistent inflammatory response. The immune system sends waves of white blood cells to the infection site, but the bacterium isn’t easily cleared. The resulting chronic inflammation damages the stomach lining over time. The bacterium also produces toxins. One, called Vac-A, damages cells by causing them to form internal vacuoles. Another protein, Cag-A, stimulates the stomach’s own cells to release chemical signals that recruit even more inflammatory cells, amplifying the damage.
Beyond direct tissue injury, H. pylori disrupts the hormonal controls on acid production. The stomach has two types of regulatory cells that work in opposition: G cells release gastrin, which tells the stomach to make more acid, while D cells release somatostatin, which tells it to slow down. H. pylori suppresses D cells and stimulates G cells. The result is excess acid production that overwhelms the duodenal lining’s defenses. The bacterium also depletes glutathione, a molecule that protects cells from oxidative damage, leaving the tissue more vulnerable.
Not everyone infected with H. pylori develops ulcers. Genetic susceptibility, the specific strain of bacterium, and environmental factors all influence whether the infection stays silent or progresses to an ulcer.
Pain Relievers and Anti-Inflammatory Drugs
Nonsteroidal anti-inflammatory drugs, commonly called NSAIDs, are the second leading cause of duodenal ulcers. This category includes over-the-counter medications like ibuprofen, naproxen, and aspirin, as well as prescription-strength versions. Their ulcer-causing potential has nothing to do with the pills physically touching the duodenum. The damage is systemic.
NSAIDs work by blocking enzymes that produce prostaglandins, hormone-like compounds involved in pain and inflammation. But prostaglandins also play a critical protective role in the gut: they stimulate mucus and bicarbonate secretion, maintain blood flow to the lining, and promote cell repair. When NSAID use suppresses prostaglandin production body-wide, the duodenal lining loses these defenses.
There’s also a direct chemical mechanism. Acidic NSAIDs remain uncharged in the low-pH environment of the stomach and upper intestine, allowing them to slip through cell membranes. Once inside the cells, the neutral internal pH causes the drug molecules to become charged and trapped, a process called ion trapping. This accumulation disrupts the cell’s energy-producing mitochondria, increases permeability of the intestinal barrier, and sets off a cycle of low-grade inflammation that can progress to erosions and ulcers.
The risk increases with higher doses, longer duration of use, and combining multiple NSAIDs. Taking NSAIDs alongside blood thinners or corticosteroids raises the risk further. People over 65 and those with a history of ulcers are especially vulnerable.
Smoking and Duodenal Ulcers
Smoking increases the risk of developing duodenal ulcers and slows their healing once they form. The relationship between nicotine and the gut is complex. Research in healthy volunteers has shown that nicotine reduces the volume of gastric secretions in a dose-dependent manner. However, its broader effects on the body work against ulcer healing: smoking impairs blood flow to the gut lining, weakens the mucus barrier, and reduces bicarbonate secretion in the duodenum.
Smokers with H. pylori infections are more likely to develop ulcers than nonsmokers with the same infection, and their ulcers are more likely to recur after treatment. Quitting smoking measurably improves ulcer healing rates.
Genetic Susceptibility
Some people are genetically more prone to duodenal ulcers. A large genome-wide study of over 456,000 people identified eight specific gene regions associated with peptic ulcer disease. These genes are involved in susceptibility to H. pylori infection, the body’s response to infection-related damage, gastric acid secretion, and gut motility. Several of the identified genes, including MUC1 and MUC6, code for mucins, the proteins that form the protective mucus barrier. Others, like GAST and CCKBR, are directly involved in gastrin signaling and acid production.
This helps explain why ulcers sometimes run in families and why two people with the same H. pylori infection can have very different outcomes. Having a first-degree relative with peptic ulcer disease roughly triples your own risk.
Zollinger-Ellison Syndrome
In rare cases, duodenal ulcers are caused by a condition called Zollinger-Ellison syndrome. Small tumors called gastrinomas, usually forming in the pancreas or duodenum, release massive amounts of gastrin. Normally, your body releases a small pulse of gastrin after eating to trigger stomach acid production. Gastrinomas flood the system with gastrin continuously, causing the stomach to produce far more acid than the duodenal lining can handle.
The ulcers from Zollinger-Ellison syndrome tend to be more severe, more numerous, and more resistant to standard treatment than typical duodenal ulcers. Without treatment, the excess acid can cause bleeding or perforation in the upper digestive tract. This condition accounts for a small fraction of all duodenal ulcers, but it’s an important diagnosis to consider when ulcers don’t respond to conventional therapy or keep coming back despite treatment.
How Duodenal Ulcer Pain Feels
The hallmark symptom is a burning or gnawing pain in the upper abdomen, typically between the belly button and the breastbone. For many people, the pain is worse on an empty stomach or during the night and improves briefly after eating. This pattern reflects the cycle of acid exposure: food temporarily buffers the acid, but once digestion is complete, the unprotected ulcer is exposed again. Some people experience the opposite, with eating making pain worse, so the timing alone isn’t a reliable way to self-diagnose.
Other common symptoms include bloating, nausea, and a feeling of fullness after small meals. More concerning signs, like vomiting blood, dark or tarry stools, or sudden sharp abdominal pain, suggest a complication such as bleeding or perforation and need immediate medical attention.
How Duodenal Ulcers Are Treated
Treatment depends on the cause. If H. pylori is present, eradicating the infection is the priority. Current guidelines from the American College of Gastroenterology recommend a 14-day course of combination therapy as the first-line approach for patients who haven’t been treated before. This involves an acid-suppressing medication taken twice daily alongside bismuth and two antibiotics. The specific antibiotic combination matters because H. pylori resistance to certain antibiotics has risen significantly in recent years, and older regimens that relied heavily on clarithromycin are no longer recommended unless testing confirms the bacteria are sensitive to it.
For NSAID-caused ulcers, the most effective step is stopping the offending medication. An acid-suppressing medication is typically prescribed for four to eight weeks to allow the ulcer to heal. If you need ongoing pain relief, your doctor can help identify alternatives that carry less risk to your gut lining.
Regardless of the cause, reducing acid exposure gives the ulcer time to heal. Most duodenal ulcers heal completely within a few weeks of appropriate treatment. Recurrence is common if the underlying cause isn’t addressed: if H. pylori isn’t fully eradicated, or if NSAID use continues, the ulcer is likely to come back.