Yes, Helicobacter pylori (H. pylori) is a bacterium. It is one of the most common bacterial infections in humans, colonizing the stomach lining of roughly half the world’s population. Most people who carry it never develop symptoms, but in about 10% to 15% of those infected, it causes peptic ulcers, and it is a strong risk factor for certain types of stomach cancer.
What Kind of Bacterium Is H. Pylori
H. pylori belongs to a class of bacteria called epsilon-proteobacteria. Under a microscope, it has a distinctive twisted, helical shape (which is where the name “Helicobacter” comes from), though some strains look more like curved rods. That corkscrew shape is not just decorative. It helps the bacterium burrow through the thick mucus layer that lines your stomach, allowing it to reach the tissue underneath where conditions are less harsh.
H. pylori is microaerophilic, meaning it needs oxygen to survive but only in small amounts, far less than what’s in the air you breathe. This preference matches its niche: buried in stomach mucus, where oxygen levels are low but not zero.
How It Survives Stomach Acid
Your stomach is one of the most hostile environments in the body, with a pH low enough to break down food and kill most swallowed microbes. H. pylori gets around this with an enzyme called urease, which breaks down urea (a natural waste product present in the stomach) into ammonia and carbon dioxide. The ammonia neutralizes the acid in the bacterium’s immediate surroundings, creating a small protective bubble of near-neutral pH. This lets H. pylori survive long enough to reach the mucus layer, where acidity is already lower, and set up a permanent home.
How H. Pylori Spreads
H. pylori passes from person to person, most often within households and during childhood. The exact routes are still being refined, but three pathways have strong evidence behind them: fecal-oral (contaminated water or food), oral-oral (saliva), and gastric-oral (contact with vomit). CDC research on household transmission found that exposure to an infected person’s vomit explained more than half of all new infections tracked in the study, and over 70% of the most clearly documented cases. This makes sense, since gastroenteritis episodes can temporarily flush the bacterium out of the stomach in high numbers.
Infection is more common in areas with crowded living conditions or limited access to clean water, and most people acquire it before age 10. Once established, H. pylori can persist for decades if untreated.
What H. Pylori Does to the Stomach
Most carriers have no symptoms at all. The bacterium triggers a chronic, low-grade inflammation of the stomach lining (gastritis), but this inflammation is often silent. Problems arise when the infection erodes the protective mucus barrier enough to let stomach acid damage the tissue directly.
About 10% to 15% of infected people develop a peptic ulcer, either in the stomach or the upper part of the small intestine. Symptoms typically include a burning or gnawing pain in the upper abdomen, bloating, nausea, and sometimes unintentional weight loss. H. pylori infection is also classified as a strong risk factor for gastric cancer, particularly a type called intestinal-type adenocarcinoma and a rare stomach lymphoma called MALT lymphoma. The vast majority of infected people will never develop cancer, but the long-term inflammatory damage increases the odds.
How H. Pylori Is Diagnosed
The most common noninvasive test is the urea breath test. You swallow a small amount of specially labeled urea. If H. pylori is present in your stomach, its urease enzyme breaks down the urea, releasing labeled carbon dioxide that you then exhale. A breath sample picks this up. The test is highly accurate: sensitivity around 93% to 99% and specificity around 96% to 98%, depending on the comparison method used. It works well both for initial diagnosis and for confirming whether treatment successfully cleared the infection.
A stool antigen test is another noninvasive option, detecting H. pylori proteins in a stool sample. If an upper endoscopy is being performed for other reasons, a small tissue sample from the stomach lining can be tested directly through biopsy.
How the Infection Is Treated
H. pylori is treated with a combination of antibiotics and an acid-suppressing medication, taken together for 14 days. The reason for multiple antibiotics is simple: the bacterium has become increasingly resistant to single drugs, and combination therapy dramatically improves the odds of clearing it completely.
The current preferred approach, recommended by the American College of Gastroenterology, uses four medications at once: an acid suppressor, tetracycline, metronidazole, and a bismuth compound (the active ingredient in products like Pepto-Bismol). This regimen replaced an older three-drug combination that relied on clarithromycin, because resistance to that antibiotic has climbed sharply worldwide. In Europe, clarithromycin resistance ranges from 12% to 22%. In parts of Asia, it reaches as high as 92%. Metronidazole resistance is even more widespread globally, though the four-drug regimen can partially overcome it by using higher doses and longer treatment.
After finishing treatment, your doctor will typically retest you (usually with the breath test) to confirm the bacteria has been eliminated. If the first round fails, alternative antibiotic combinations are available, though options narrow with each attempt. Successful eradication heals most H. pylori-related ulcers and substantially lowers the risk of future stomach problems.