H. pylori (Helicobacter pylori) is a type of bacteria that infects the stomach lining, where it can survive for decades and cause chronic inflammation. Roughly 44% of adults worldwide currently carry the infection, though many never develop symptoms. When it does cause problems, H. pylori is the leading cause of stomach ulcers and a major risk factor for stomach cancer.
How H. pylori Survives in Your Stomach
Your stomach produces hydrochloric acid strong enough to break down food, which should make it an impossible place for bacteria to live. H. pylori gets around this with a clever chemical trick: it produces an enzyme that converts a naturally occurring compound called urea into ammonia. Ammonia is alkaline, so it neutralizes the acid in the bacteria’s immediate surroundings, creating a small pocket of near-neutral pH where H. pylori can thrive.
This system is remarkably precise. The bacteria have a special channel in their cell walls that only opens when the environment becomes acidic. When stomach acid rises, the channel opens, letting urea flood in and ammonia production ramp up. When conditions are already neutral, the channel stays closed. This on-demand acid defense lets H. pylori maintain a stable environment inside and around itself, even in one of the harshest environments in the human body.
The bacteria’s spiral shape also plays a role. That corkscrew form lets H. pylori burrow into the thick mucus layer that coats the stomach wall, where acid levels are already lower. Once embedded in that mucus, the bacteria are well protected and difficult for the immune system to reach.
How H. pylori Spreads
H. pylori passes from person to person, most often within families and households. The three main transmission routes are fecal-to-oral (through contaminated water or poor hand hygiene), oral-to-oral (through saliva), and gastric-to-oral (through vomit). The bacteria can be recovered most reliably from vomit and from stool during episodes of rapid gut transit like diarrhea.
Household exposure matters a great deal. CDC research found that living with an infected person who has a stomach illness increases the risk of new infection nearly fivefold. Vomiting posed a greater risk than diarrhea alone, with a sixfold increase in odds. About 75% of new infections in the study were traced back to exposure to a sick household member. Crowded living conditions and limited access to clean water are the biggest environmental risk factors, which is why infection rates are higher in lower-income regions.
Most people acquire H. pylori during childhood. Global prevalence has dropped over the past few decades, from about 53% before 1990 to 44% in adults today, but it remains around 35% in children and adolescents.
Symptoms of an H. pylori Infection
Most people with H. pylori have no symptoms at all. The bacteria can live quietly in the stomach lining for years or even a lifetime without causing noticeable problems. When symptoms do appear, they typically result from the inflammation or ulcers the infection creates over time.
Symptomatic H. pylori infection usually shows up as a burning or gnawing pain in the upper abdomen, often between meals or during the night when the stomach is empty. Other common signs include bloating, nausea, feeling full after eating only a small amount, frequent burping, and a general sense of indigestion. These symptoms overlap with many other digestive conditions, which is why testing is needed to confirm whether H. pylori is the cause.
Long-Term Risks and Complications
Left untreated, chronic H. pylori infection can lead to peptic ulcers, which are open sores in the stomach lining or the upper portion of the small intestine. These ulcers are a significant source of illness worldwide and can sometimes cause bleeding or perforation if they go unmanaged.
The more serious long-term concern is stomach cancer. Consistent evidence links chronic H. pylori infection to gastric adenocarcinoma (the most common type of stomach cancer) and gastric MALT lymphoma, a cancer of the immune tissue in the stomach wall. Nearly all patients diagnosed with gastric MALT lymphoma show signs of H. pylori infection. A large clinical trial in China, where stomach cancer rates are high, found that just two weeks of antibiotic treatment to clear the infection reduced stomach cancer incidence by nearly 50% over 22 years of follow-up. That finding highlights how much of the cancer risk is directly tied to the ongoing presence of the bacteria.
How H. pylori Is Diagnosed
Several tests can detect an active H. pylori infection, and they fall into two categories: invasive and non-invasive.
The most common non-invasive option is the urea breath test. You swallow a small amount of a specially labeled urea compound, and if H. pylori is present, the bacteria break it down and produce carbon dioxide that can be measured in your breath. Meta-analyses put the sensitivity of this test around 88% and the specificity around 85%, meaning it correctly identifies most infections while producing relatively few false positives. Stool antigen testing is another non-invasive alternative that looks for H. pylori proteins in a stool sample.
For patients already undergoing an upper endoscopy (where a thin camera is passed into the stomach), doctors can take small tissue samples directly from the stomach wall. Combining a rapid urease test on the tissue with a microscopic examination of biopsies from two different sites gives the most reliable diagnosis. The tradeoff is that H. pylori doesn’t always distribute evenly across the stomach, so a biopsy from one spot can occasionally miss an infection that a biopsy from another spot would catch.
Treatment: A Multi-Drug Approach
H. pylori can’t be eliminated with a single antibiotic. Current guidelines from the American College of Gastroenterology recommend bismuth quadruple therapy as the preferred first-line treatment when antibiotic susceptibility hasn’t been tested. This regimen combines a stomach acid reducer with bismuth (which has direct antibacterial effects) and two antibiotics, taken for 14 days.
The 14-day course matters. Shorter regimens have lower success rates because H. pylori is notoriously difficult to fully eradicate from the stomach’s protective mucus layer. If the first round of treatment doesn’t work, a modified version of the same approach or an alternative combination is used for another 14 days.
Why Antibiotic Resistance Is a Growing Problem
One of the biggest challenges in treating H. pylori today is rising antibiotic resistance. Clarithromycin, once a cornerstone of treatment, now has resistance rates above 15% in 24 out of 31 countries surveyed in a recent global analysis. In parts of Asia, clarithromycin resistance reaches as high as 92%. Levofloxacin, commonly used as a second-line option, faces similar problems, with resistance exceeding 15% in 18 out of 31 countries and climbing as high as 66% in parts of Africa.
Amoxicillin remains a bright spot, with resistance under 2% in most countries, though some African nations report rates above 90%. Because of these patterns, current guidelines now recommend that clarithromycin and levofloxacin only be used when testing confirms the bacteria are susceptible. Only four countries (Spain, Germany, Japan, and South Korea) currently have regular antibiotic resistance surveillance programs for H. pylori, which means many regions are essentially treating blind.
Bismuth-based regimens remain the most effective option globally, partly because resistance to bismuth is extremely rare. However, more than a billion people worldwide live in areas where bismuth-based medications aren’t available, leaving them reliant on regimens with lower success rates.
Reducing Your Risk
Because H. pylori spreads through contaminated water, food, and close personal contact, prevention comes down to basic hygiene. Washing your hands thoroughly with soap and water for at least 20 seconds before eating and after using the bathroom is the most effective everyday measure. If you live in or travel to areas with unreliable water treatment, using clean water for both drinking and food preparation significantly lowers risk. These simple steps are especially important for protecting children, who are the most likely to acquire new infections.