Gastritis, the inflammation of your stomach lining, can be triggered by infections, medications, alcohol, autoimmune conditions, and physical stress on the body. Some causes develop over years without symptoms, while others strike within hours. Understanding which cause is behind your gastritis matters because treatment depends entirely on the trigger.
H. pylori Infection
The single most common cause of chronic gastritis worldwide is a spiral-shaped bacterium called H. pylori. This organism has evolved specifically to survive in the harsh acid environment of the stomach, and it infects people more frequently in developing countries than in industrialized ones.
H. pylori attaches directly to gastric cells and begins disrupting the stomach’s normal chemistry. It depletes glutathione, a molecule your cells rely on to manage immune responses and protect against oxidative damage. At the same time, it manipulates the cells that regulate acid production: it suppresses the cells that put the brakes on acid secretion while stimulating the cells that ramp it up. The result is a stomach producing more acid with fewer defenses. Over time, this chronic irritation can progress from surface-level inflammation to deeper damage. Many people carry H. pylori for years without realizing it, because early gastritis often produces no noticeable symptoms.
Pain Relievers and Other Medications
NSAIDs like ibuprofen, aspirin, and naproxen are one of the most common causes of acute gastritis, especially with regular use. These drugs work by blocking an enzyme called COX-1, which has a side job beyond pain signaling: it helps produce compounds called prostaglandins that protect the stomach lining. When prostaglandin levels drop, your stomach loses its normal defenses. Blood flow to the lining decreases, the protective mucus layer thins, and the stomach’s muscular contractions can become abnormally strong, all of which combine to create the conditions for erosion and inflammation.
This isn’t limited to high doses. Even standard over-the-counter amounts taken regularly can gradually wear down the gastric lining. The risk increases with age, higher doses, and combining NSAIDs with alcohol or corticosteroids.
Alcohol
Excessive alcohol consumption is a classic trigger for acute erosive gastritis, meaning it causes visible damage and bleeding in the stomach lining. Ethanol is directly toxic to gastric cells. It ramps up the production of gastric acid by increasing the activity of acid-secreting receptors, flooding the stomach with hydrochloric acid at concentrations that are fatal to cells.
Beyond the acid surge, alcohol causes white blood cells to infiltrate the tissue beneath the stomach’s surface layer, creating an inflammatory response that compounds the chemical damage. Binge drinking can cause sudden, severe gastritis, but chronic moderate-to-heavy drinking produces a slower, cumulative erosion of the lining.
Autoimmune Gastritis
In autoimmune gastritis, your immune system mistakenly attacks the acid-producing parietal cells of the stomach. The specific target is a protein called H+/K+-ATPase, which is the molecular pump these cells use to secrete hydrochloric acid. Between 75% and 95% of patients with autoimmune gastritis carry antibodies against this protein.
As parietal cells are destroyed over time, acid production drops and the stomach lining gradually thins. This form of gastritis is relatively uncommon, affecting an estimated 0.1% to 2% of the general population, though prevalence rises to around 2.5% to 3% in people over 60. Because parietal cells also help you absorb vitamin B12, autoimmune gastritis frequently leads to B12 deficiency and, in severe cases, pernicious anemia.
Severe Physical Stress
Major physiological stress on the body, not everyday emotional stress, can trigger a distinct form called stress-induced gastritis. This typically happens in critically ill patients: those recovering from major surgery, severe burns, traumatic injuries, or organ failure.
The mechanism involves a cascade of changes. The body’s stress response releases hormones that constrict blood vessels supplying the stomach, reducing blood flow to the lining. At the same time, levels of chemical messengers that stimulate acid production spike, so the stomach is producing more acid while receiving less blood to nourish and repair its cells. The reduced blood flow also generates reactive oxygen species, which damage the DNA of mucosal cells directly. Meanwhile, the body slows gastric cell renewal, meaning the lining can’t replace damaged cells at its normal rate. The combination, more acid, less blood flow, impaired repair, is what makes this form of gastritis develop so rapidly in hospitalized patients.
Bile Reflux
Bile is produced by your liver and normally flows from the gallbladder into the small intestine, well downstream of the stomach. But when the valve between the stomach and small intestine doesn’t close properly, bile can wash backward into the stomach. This is especially common after certain stomach or gallbladder surgeries.
Bile acids and a compound called lysolecithin dissolve the protective phospholipid and cholesterol layer on the stomach’s surface. Once this barrier breaks down, hydrogen ions from gastric acid can penetrate directly into the stomach wall tissue, causing inflammation and damage. Bile reflux gastritis tends to be chronic and can be tricky to manage because standard acid-reducing medications don’t address the bile component.
Diet and Irritants
The relationship between food and gastritis is less straightforward than most people assume. Spicy foods, acidic beverages, and fried or salty foods are frequently associated with gastritis symptoms like stomach pain and bloating, but the evidence that they directly cause the underlying inflammation is limited. Research from South India found that patients with chronic gastritis commonly reported that spicy and irritating foods worsened their symptoms, and irregular meal timing and portion sizes were also associated with increased stomach distress. However, many patients had already changed their diets in response to their symptoms, making it difficult to determine whether these foods triggered the gastritis or simply aggravated existing inflammation.
What’s clearer is that certain dietary habits can compound other risk factors. Eating irregularly while taking NSAIDs, or consuming heavily spiced meals alongside alcohol, creates a harsher environment for an already-compromised stomach lining.
Rare Immune-Related Forms
Eosinophilic gastritis occurs when a type of white blood cell called eosinophils accumulates in the stomach wall in abnormally high numbers. It’s rare, affecting roughly 6.3 per 100,000 people. About 38.5% of those diagnosed also have an allergic condition such as rhinitis (28% to 30%) or asthma (16%). This overlap with allergies suggests an immune-driven process, though some patients have no allergic history at all, and researchers suspect an autoimmune component may play a role in certain cases.
How Gastritis Is Diagnosed
The gold standard for diagnosing gastritis is endoscopy with biopsy, where a thin camera is passed into the stomach and small tissue samples are taken. A standardized system called the Sydney Classification recommends taking at least five biopsies from specific locations in the stomach, including two from the lower portion (antrum), two from the upper portion (corpus), and one from the curved area between them. Under a microscope, pathologists look for specific patterns of inflammatory cells to confirm gastritis and determine its severity and likely cause.
This matters because different causes look different under the microscope. H. pylori infection, autoimmune destruction, and bile reflux each leave distinctive patterns that guide treatment in completely different directions.
When Gastritis Becomes a Longer-Term Concern
Most acute gastritis resolves once the trigger is removed: stop the NSAID, treat the infection, cut back on alcohol. Chronic gastritis, particularly the type that causes the stomach lining to thin and lose its normal glandular structure (called atrophic gastritis), carries a small but real cancer risk that warrants monitoring.
In a Korean study of over 2,100 people with atrophic gastritis, the crude incidence of gastric cancer was 1.7% over the observation period. A large Dutch study found the annual cancer incidence for atrophic gastritis patients was about 0.1% per year. A British study following high-risk patients found that 8.4% developed gastric cancer over 10 years. These numbers are low enough that most people with atrophic gastritis will never develop cancer, but high enough that periodic surveillance with endoscopy is typically recommended, especially if the atrophy is extensive or if you’re also positive for H. pylori.