Stomach inflammation, called gastritis, happens when something damages or weakens the protective mucus lining that shields your stomach wall from its own acid. The two most common causes are a bacterial infection called H. pylori and regular use of common pain relievers like ibuprofen or aspirin. But several other triggers can break down that barrier too, from heavy alcohol use to severe physical stress to your own immune system turning against stomach cells.
How the Stomach’s Protective Barrier Works
Your stomach produces highly acidic digestive juices, yet the organ doesn’t dissolve itself because a thick layer of mucus sits between the acid and the stomach wall. This mucus barrier is maintained by chemical signals called prostaglandins, along with nitric oxide and nerve stimulation from the vagus nerve. When this barrier is intact, acid stays where it belongs. When something disrupts it, acid diffuses backward into the exposed tissue and causes damage, swelling, and pain.
Nearly every cause of gastritis works through this same basic mechanism: something compromises the mucus layer, and the stomach’s own acid does the rest.
H. Pylori Infection
Helicobacter pylori is the single most common cause of chronic stomach inflammation worldwide. Recent global data published in the journal Gastroenterology estimates that about 44% of adults and 35% of children carry this bacterium. Rates vary dramatically by region, with the highest prevalence in Africa and the Eastern Mediterranean and the lowest in Europe.
H. pylori survives in one of the harshest environments in the body by producing an enzyme called urease, which breaks down urea into ammonia and neutralizes the acid in its immediate surroundings. The bacterium carries urease both on its outer surface and inside its cells. Internally, the chemical reaction also generates energy that powers the bacterium’s whip-like tail, letting it swim through the thick mucus gel and burrow into the stomach lining. Once embedded, it triggers a chronic inflammatory response that can persist for decades if untreated.
Most people with H. pylori never develop symptoms. But in those who do, the ongoing inflammation can progress over years from simple gastritis to a thinning of the stomach lining (atrophic gastritis) and eventually to precancerous changes. A large observational study published in The BMJ tracked these stages: roughly 1 in 85 people with gastritis developed stomach cancer within 20 years, compared to 1 in 50 with atrophic gastritis and 1 in 39 with a more advanced change called intestinal metaplasia. These numbers are still relatively low in absolute terms, but they illustrate why identifying and treating H. pylori matters.
Pain Relievers and NSAIDs
Nonsteroidal anti-inflammatory drugs, the category that includes ibuprofen, naproxen, and aspirin, are the second most common cause of gastritis. These medications work by blocking enzymes called COX-1 and COX-2, which reduces pain and swelling throughout the body. The problem is that these same enzymes produce the prostaglandins your stomach needs to maintain its mucus barrier.
When NSAIDs suppress prostaglandin production, the mucus layer thins, blood flow to the stomach lining decreases, and the tissue becomes vulnerable to acid damage. Research initially pointed to COX-1 inhibition as the primary culprit, but more recent studies show that blocking both COX-1 and COX-2 together is what actually causes injury. COX-2 appears to act as a backup system: when COX-1 is shut down, COX-2 ramps up to keep producing protective prostaglandins. Medications that block both enzymes simultaneously eliminate that safety net.
This is why occasional use of an NSAID rarely causes problems, but daily or long-term use, especially without food or stomach-protecting medication, significantly raises the risk of gastritis and ulcers.
Alcohol
Alcohol is a direct chemical irritant to stomach tissue. Because ethanol dissolves easily in fat, it passes rapidly through the outer membranes of stomach lining cells and disrupts them from the inside out. Animal studies show that concentrations above 20% (roughly the strength of a fortified wine or liquor) cause visible erosions in the stomach, with damage increasing in proportion to alcohol strength. Pure ethanol causes extensive tissue death within minutes.
Even lower concentrations cause measurable harm. At just 4 to 5% alcohol (about the strength of a light beer), researchers can detect changes in the electrical charge across the stomach lining, a sign that the barrier is becoming leaky. At 12.5%, the equivalent of wine, visible redness and small bleeding spots appear under a microscope. What happens at the cellular level is that alcohol disrupts the stomach’s ability to pump sodium out of cells. Sodium, water, and other ions accumulate inside the cells, causing them to swell and rupture. This opens gaps in the lining that allow acid and other irritants to penetrate deeper into the tissue.
Severe Physical Stress
Gastritis doesn’t always come from something you swallowed. Severe physiological stress, the kind caused by major trauma, extensive burns, brain injuries, sepsis, or major surgery, can trigger acute stomach inflammation even in people with no prior stomach problems.
The mechanism is straightforward: during critical illness, blood flow is diverted away from the digestive tract to support vital organs. This reduced blood supply starves the stomach lining of oxygen and nutrients, and the mucus barrier breaks down. Interestingly, acid production during stress gastritis is typically normal or even decreased. The problem isn’t too much acid; it’s that the protective layer has collapsed and even normal acid levels cause damage.
These stress-related lesions have specific names depending on the trigger. Burns produce what are called Curling ulcers. Traumatic brain injuries produce Cushing ulcers. Both can develop rapidly, sometimes within hours of the initial injury.
Autoimmune Gastritis
In autoimmune gastritis, the immune system mistakenly produces antibodies that attack the stomach’s acid-producing cells, called parietal cells. These antibodies target the cellular machinery that generates stomach acid as well as a protein called intrinsic factor, which is essential for absorbing vitamin B12 from food.
The condition is inherited and tends to progress slowly. As more parietal cells are destroyed, the stomach gradually loses its ability to produce acid. More critically, the loss of intrinsic factor leads to vitamin B12 deficiency, which can cause a specific type of anemia called pernicious anemia. Left unaddressed, B12 deficiency also damages the nervous system, causing numbness, balance problems, and cognitive changes. Autoimmune gastritis is less common than H. pylori or NSAID-related gastritis, but it’s important to identify because the B12 deficiency it causes requires lifelong supplementation.
Bile Reflux
Bile is produced by the liver and stored in the gallbladder to help digest fats in the small intestine. Normally, a muscular valve called the pyloric valve sits at the stomach’s exit and opens just enough to release tiny amounts of partially digested food, about a teaspoon at a time. It stays closed tightly enough to prevent digestive juices from flowing backward.
When this valve doesn’t close properly, bile washes back into the stomach and irritates the lining. Stomach surgery is the most common reason this happens, particularly partial stomach removal or gastric bypass. Gallbladder removal also significantly increases bile reflux. Peptic ulcers can physically obstruct the valve and prevent it from sealing. Unlike acid reflux, bile reflux doesn’t respond to acid-suppressing medications because the irritant is bile, not acid.
How Gastritis Is Diagnosed
Symptoms alone can’t confirm gastritis because the burning, nausea, and upper abdominal pain it causes overlap with many other conditions. The definitive diagnosis comes from an upper endoscopy, where a thin, flexible camera is passed through the mouth into the stomach. During the procedure, the doctor takes small tissue samples (biopsies) from the stomach lining. A pathologist examines these under a microscope to confirm inflammation, identify the cause, and check for precancerous changes.
Testing for H. pylori can also be done through a breath test, stool test, or blood test, which are often used as a first step before endoscopy. If H. pylori is found, treatment with a combination of antibiotics and acid-suppressing medication clears the infection in most people. For NSAID-related gastritis, stopping or reducing the medication is usually enough for the stomach to heal, sometimes with the help of acid-reducing drugs during recovery. Autoimmune gastritis requires ongoing monitoring and B12 supplementation rather than a one-time fix.
Why Chronic Inflammation Matters
A single episode of gastritis from a night of heavy drinking or a short course of ibuprofen typically heals on its own once the irritant is removed. Chronic gastritis is a different story. When inflammation persists for months or years, the stomach lining gradually changes. Acid-producing glands thin out, and the tissue can develop cellular patterns that aren’t normally found in the stomach.
The BMJ study that followed patients over 20 years mapped this progression clearly. The annual risk of stomach cancer climbed with each stage: people with a normal stomach lining had the lowest risk, those with simple gastritis had about 1.8 times that baseline risk, atrophic gastritis raised it to 2.8 times, and intestinal metaplasia pushed it to 3.4 times. These are still small absolute numbers for any individual, but they underscore why chronic gastritis, particularly from untreated H. pylori, is worth addressing rather than ignoring.