H. pylori causes a range of digestive problems, from chronic stomach inflammation to peptic ulcers and, in a small percentage of cases, stomach cancer. Most people infected with H. pylori never develop symptoms, but when the bacterium does cause damage, the effects can be serious and long-lasting.
How H. Pylori Damages the Stomach
H. pylori survives in the harsh acid of the stomach by producing an enzyme that generates ammonia, which neutralizes acid in its immediate surroundings. That ammonia is also toxic to the cells lining the stomach. At the same time, the bacterium releases substances that break down the protective mucus layer coating the stomach wall, stripping away the barrier that normally keeps acid from reaching delicate tissue underneath. Once that barrier is compromised, stomach acid can seep back into the exposed lining and cause direct injury.
Not all strains of H. pylori are equally harmful. Some produce a protein that triggers a stronger inflammatory response in the stomach lining, and people infected with these strains face a higher risk of developing ulcers or cancer. Other strains produce a toxin that damages stomach cells from the inside, causing them to form large internal bubbles that disrupt normal function. The strain you carry partly determines whether the infection stays silent or progresses to something more serious.
Gastritis and Peptic Ulcers
The most common consequence of H. pylori infection is chronic gastritis, a persistent inflammation of the stomach lining. This can simmer for years without causing noticeable symptoms. When symptoms do appear, they typically include a burning or aching pain in the upper abdomen (often worse on an empty stomach), bloating, frequent burping, nausea, loss of appetite, and unexplained weight loss.
If the inflammation is severe or prolonged enough, it can erode the stomach lining or the upper portion of the small intestine, creating open sores called peptic ulcers. These ulcers cause sharper pain and can bleed, sometimes producing dark or tarry stools. H. pylori is the leading infectious cause of peptic ulcers worldwide, and eradicating the infection is the primary way to heal these ulcers and prevent them from returning.
Stomach Cancer and Lymphoma
Long-term H. pylori infection increases the risk of gastric adenocarcinoma, the most common type of stomach cancer. According to the National Cancer Institute, people with chronic infections have an elevated risk of cancer developing in the main body of the stomach. In parts of Asia and other regions where stomach cancer rates are high, the infection also raises the risk of cancer at the top of the stomach, near the esophagus.
H. pylori is also linked to a rare type of cancer called gastric MALT lymphoma, which develops in the immune tissue of the stomach lining. Nearly all patients diagnosed with this lymphoma show signs of H. pylori infection, and the risk is substantially higher in infected people. The encouraging finding is that in many early-stage cases, treating the H. pylori infection alone can cause this lymphoma to regress without chemotherapy or radiation.
It’s worth noting that stomach cancer remains uncommon relative to the huge number of people carrying H. pylori. Most infected individuals never develop cancer. But because the bacterium is classified as a definite carcinogen, identifying and treating the infection is one of the few ways to actively reduce stomach cancer risk.
Effects Beyond the Stomach
H. pylori’s impact isn’t limited to the digestive tract. The infection is associated with several blood-related conditions that many doctors, particularly in pediatric practice, may not immediately connect to a stomach bug. Iron deficiency anemia is one of the most recognized, likely because chronic stomach inflammation impairs iron absorption. Vitamin B12 deficiency leading to a form of anemia called megaloblastic anemia can also result from long-standing infection.
Another condition linked to H. pylori is immune thrombocytopenic purpura (ITP), a disorder where the body’s immune system destroys its own platelets, the blood cells responsible for clotting. Some studies have found lower platelet counts in patients with both ITP and H. pylori infection, and platelet numbers have improved after the infection was cleared. In one reported case, a teenager with H. pylori-related stomach damage saw both her anemia and low platelet count resolve completely once the bacteria were eradicated.
How H. Pylori Spreads
H. pylori passes between people through contact with infected saliva, vomit, or stool. Infection clusters within families, and conditions of crowding and poor sanitation increase risk. CDC-published research found that exposure to a household member who had gastroenteritis while carrying H. pylori increased the risk of new infection nearly fivefold. Vomiting was a bigger transmission risk than diarrhea alone, with a sixfold increase in odds. About 75% of new household infections were traced back to contact with a sick, infected family member.
Most people acquire H. pylori during childhood, and once established, the infection persists for life unless treated with antibiotics. It does not clear on its own.
How the Infection Is Detected
If you’re being tested for H. pylori, your doctor will likely use one of two noninvasive methods. A urea breath test has you swallow a specially labeled substance; if H. pylori is present, the bacteria break it down and produce a gas detected in your breath. The more commonly used version of this test has a sensitivity around 96% and specificity around 93%, making it highly reliable. A stool antigen test, which detects H. pylori proteins in a stool sample, achieves accuracy above 90% and is often used in settings where breath testing isn’t available.
When an upper endoscopy is performed (usually because symptoms are severe or an ulcer is suspected), tissue samples can be tested directly. A rapid urease test applied to biopsied tissue reaches about 90% sensitivity and 95 to 100% specificity. Growing the bacteria in a lab from a biopsy sample is the most specific method (100%), though it’s less sensitive and takes longer, so it’s typically reserved for cases where antibiotic resistance needs to be identified.
Treatment Challenges
H. pylori is treated with a combination of antibiotics and an acid-reducing medication, typically taken for 10 to 14 days. The challenge is that antibiotic resistance is rising worldwide. Resistance to one of the most effective antibiotics used against H. pylori now exceeds 15% in the majority of countries studied. In parts of Asia, resistance to this drug ranges from 7% to over 90%. Resistance to another commonly used antibiotic class is the highest of any drug used in treatment.
This means first-line treatment doesn’t always work. If your initial course of antibiotics fails to clear the infection, your doctor may need to try a different combination or, in some cases, test the specific strain you carry to determine which antibiotics it’s still vulnerable to. Confirming that the infection has been eradicated, usually with a breath or stool test done at least four weeks after finishing treatment, is an important step that shouldn’t be skipped.