Gastritis, the inflammation of your stomach lining, has several distinct causes ranging from bacterial infection to medication side effects to your own immune system turning against you. Globally, over 38 million people were living with gastritis and duodenitis in 2021, though the rate per 100,000 people has actually dropped about 13% since 1990. Understanding what’s behind the inflammation matters because the cause determines the treatment, and some forms carry long-term risks that others don’t.
H. pylori: The Most Common Bacterial Cause
A spiral-shaped bacterium called Helicobacter pylori is the single most frequent cause of chronic gastritis worldwide. It colonizes the stomach lining and survives in an environment that would kill most other organisms. H. pylori produces an enzyme called urease that generates ammonia, which neutralizes the acid immediately surrounding the bacterium. That ammonia is directly toxic to the cells lining your stomach.
The damage doesn’t stop there. H. pylori also releases enzymes that break down the protective mucus coating your stomach wall and disrupt the fatty layer on the surface of your stomach cells. Once that barrier is compromised, your own stomach acid can reach the exposed cells underneath, essentially digesting small patches of your own tissue. The body responds with inflammation, and if the infection persists for years (which it often does without treatment), chronic gastritis can progress to thinning of the stomach lining, precancerous changes, or ulcers.
Most people pick up H. pylori during childhood through contaminated food, water, or close contact. Many carriers never develop symptoms, but in those who do, the severity of inflammation tracks closely with the density of the bacterial infection.
Pain Relievers That Erode the Stomach
Nonsteroidal anti-inflammatory drugs, commonly called NSAIDs, are the second major cause of gastritis. This includes over-the-counter staples like ibuprofen, naproxen, and aspirin. These drugs work by blocking enzymes that produce prostaglandins, the chemical messengers responsible for pain and inflammation throughout your body. The problem is that those same prostaglandins also maintain several layers of your stomach’s defense system: they stimulate mucus production, promote blood flow to the stomach lining, and help cells repair themselves.
When you take an NSAID, prostaglandin levels drop across the board. Your stomach produces less protective mucus, blood flow to the lining decreases, and the tissue becomes more vulnerable to acid damage. Occasional use rarely causes problems for most people, but regular or heavy use, particularly in older adults or those taking blood thinners, can lead to erosive gastritis, ulcers, and bleeding. Even newer, more selective anti-inflammatory drugs haven’t fully eliminated this risk.
Autoimmune Gastritis
In autoimmune gastritis, your immune system mistakenly attacks the acid-producing cells in your stomach, called parietal cells. Your body generates antibodies against these cells and their components, gradually destroying them over months to years. This is an inherited condition, meaning it tends to run in families.
Parietal cells do two critical jobs: they secrete stomach acid, and they produce a protein called intrinsic factor that your body needs to absorb vitamin B12 from food. As these cells are destroyed, acid production drops and B12 absorption fails. The B12 deficiency that follows can cause a specific type of anemia called pernicious anemia, along with neurological symptoms like numbness, tingling, difficulty walking, and cognitive changes. These consequences can take years to develop because the body stores enough B12 to last a while, but once reserves run out, the symptoms can be serious. Autoimmune gastritis also carries an elevated long-term risk of stomach cancer, so it typically requires ongoing monitoring.
Alcohol and Chemical Irritants
Alcohol is a direct irritant to the stomach lining. Ethanol gradually erodes the mucosal barrier, and heavy or prolonged drinking can cause acute erosive gastritis, sometimes with visible bleeding. The damage tends to be dose-dependent: the more you drink and the more often you drink, the greater the injury. Binge drinking can trigger sudden, severe inflammation even in someone who doesn’t drink regularly.
Smoking also contributes to gastritis, both by impairing blood flow to the stomach lining and by increasing acid production. There’s newer evidence that e-cigarettes may pose their own risks to the gut. A UC San Diego study found that two base chemicals in all e-cigarette liquid, propylene glycol and vegetable glycerol, caused the tight junctions between gut lining cells to loosen. These junctions normally act like zippers holding cells together to form a barrier. When they break down, bacteria and other molecules can leak through, triggering chronic inflammation. This occurred even with nicotine-free e-cigarettes, suggesting the vapor itself is the problem.
Bile Reflux
Bile is a digestive fluid made by your liver and stored in your gallbladder. It’s supposed to flow downward into your small intestine, never backward into your stomach. A muscular valve at the bottom of your stomach normally prevents this, opening just enough to release tiny amounts of digested food (about a teaspoon at a time) while keeping bile out. When this valve doesn’t close properly, bile washes back into the stomach and inflames the lining.
Bile reflux gastritis is especially common after certain surgeries. People who’ve had part or all of their stomach removed, or who’ve undergone gastric bypass for weight loss, are at highest risk because the surgery alters or bypasses the valve entirely. People who’ve had their gallbladder removed also experience significantly more bile reflux than those who haven’t. Unlike acid reflux, bile reflux doesn’t respond to acid-blocking medications, which makes it a distinct and sometimes frustrating condition to manage.
Stress-Related Gastritis
Severe physiological stress, not everyday emotional stress, can trigger a specific form of gastritis. This typically happens in people who are critically ill: those in intensive care with major burns, head injuries, organ failure, or recovering from major surgery. The mechanism involves reduced blood flow to the stomach lining during the body’s crisis response, leaving the tissue vulnerable to acid damage. Stress-related gastritis can develop rapidly, sometimes within hours of the triggering event, and it can cause significant bleeding.
The role of everyday psychological stress is less clear-cut. Chronic stress doesn’t directly inflame the stomach lining the way a bacterium or a drug does, but it can increase acid production, alter eating habits, drive heavier alcohol or NSAID use, and slow digestion, all of which create conditions where gastritis is more likely to develop or worsen.
Less Common Causes
Several other conditions can inflame the stomach lining, though they’re far less frequent than the causes above.
- Infections beyond H. pylori: Cytomegalovirus (CMV) can cause gastritis in people with weakened immune systems, appearing as erosions or shallow ulcers in the stomach. Fungal infections, particularly candida, can also settle in the stomach, typically in immunocompromised individuals. Another related bacterium, H. heilmannii, causes a milder form of gastritis with less inflammation than its more famous cousin.
- Iron supplements: Oral iron pills, commonly prescribed for iron-deficiency anemia, can deposit crystalline pigmented material in the stomach lining, causing erosion, ulceration, and localized tissue damage.
- Radiation therapy: Radiation directed at the upper abdomen can injure the stomach lining, causing inflammation that may persist well after treatment ends.
- Other autoimmune conditions: People with autoimmune gastritis frequently have other autoimmune disorders, including thyroid disease and type 1 diabetes, suggesting shared genetic susceptibility.
Why the Cause Matters
Gastritis isn’t a single disease with a single solution. H. pylori gastritis is treated by eliminating the bacterium. NSAID-related gastritis improves when you stop or switch the offending medication. Autoimmune gastritis can’t be reversed, but its consequences, particularly B12 deficiency, can be managed with supplementation and regular monitoring. Bile reflux may require surgical correction if medications don’t help.
The severity of gastritis also varies enormously depending on the cause. A single bout of heavy drinking might cause temporary inflammation that heals on its own within days. Decades of untreated H. pylori infection, on the other hand, can lead to progressive thinning of the stomach lining, with atrophy graded from mild (less than 30% of glands lost) to marked (more than 60% lost). Advanced atrophy and a change called intestinal metaplasia, where stomach cells start resembling intestinal cells, are both associated with increased risk of stomach cancer. Identifying the cause early gives you the best chance of stopping the damage before it progresses.