H. pylori (Helicobacter pylori) is a spiral-shaped bacterium that infects the stomach lining, affecting roughly 44% of adults worldwide. Most people with the infection never develop symptoms, but in some cases it leads to stomach ulcers, chronic inflammation, and a higher risk of stomach cancer. It’s one of the most common bacterial infections on the planet, and it often begins in childhood.
How H. Pylori Survives in Your Stomach
Your stomach is intensely acidic, hostile enough to kill most bacteria on contact. H. pylori gets around this by producing an enzyme that breaks down urea (a natural compound in stomach fluid) into ammonia. The ammonia neutralizes the acid in the bacterium’s immediate surroundings, creating a small pocket of survivable pH. This chemical trick does something else: it changes the consistency of the thick mucus layer coating your stomach wall, turning it from a gel into a thinner liquid. That shift allows H. pylori to swim freely through the mucus using a bundle of whip-like tails called flagella, eventually reaching the stomach lining where it settles in and triggers inflammation.
How It Spreads
H. pylori passes from person to person, most commonly through contact with an infected person’s vomit, saliva, or stool. In one CDC-linked study, exposure to vomit from an infected household member accounted for over half of all new infections. The infection clusters in families and is strongly tied to crowding and limited sanitation, which is why rates are higher in developing regions and why most people pick it up during childhood rather than as adults.
The bacterium has been reliably recovered from vomit and from stool during bouts of diarrhea, making gastroenteritis episodes a particularly high-risk window for household transmission.
Symptoms to Watch For
Most H. pylori infections produce no symptoms at all. You can carry the bacterium for years or even decades without knowing it. When symptoms do appear, they typically come from inflammation of the stomach lining (gastritis) or from a peptic ulcer that has formed. Common signs include:
- A burning or aching pain in the upper stomach, often worse on an empty stomach
- Frequent bloating and burping
- Nausea or loss of appetite
- Unexplained weight loss
The hallmark clue is stomach pain that flares when you haven’t eaten and improves briefly after a meal. If you notice dark or tarry stools, vomiting that looks like coffee grounds, or sharp sudden abdominal pain, those can signal a bleeding or perforated ulcer, which needs immediate medical attention.
Long-Term Risks
Left untreated over many years, H. pylori can cause damage beyond ulcers. The bacterium is classified as a definite carcinogen. The majority of gastric adenocarcinoma (the most common type of stomach cancer) and nearly all cases of a rare stomach lymphoma called MALT lymphoma are attributed to H. pylori infection. MALT lymphoma is uncommon in the U.S., with roughly one case per 100,000 people per year, but among those who develop it, signs of H. pylori infection are found in nearly every patient.
These serious outcomes remain relatively rare compared to the total number of people carrying the bacterium, but they’re the main reason doctors recommend treating the infection once it’s found, even in people without symptoms.
How It’s Diagnosed
The most accurate non-invasive test is the urea breath test. You swallow a small capsule or liquid containing a tagged form of urea. If H. pylori is present, its enzyme breaks down the urea, and the tagged carbon shows up in your breath within minutes. This test has a sensitivity around 92 to 94%, meaning it correctly identifies infection in the vast majority of cases.
A stool antigen test is another solid option, with sensitivity around 83%. It works especially well in populations where H. pylori is less common, and it’s often more convenient since it doesn’t require a special clinic visit. Blood antibody tests exist but are generally not recommended in low-prevalence populations because they produce too many false positives. They also can’t distinguish a current infection from a past one.
If you’re having an upper endoscopy for another reason, your doctor can take a small tissue sample from the stomach lining and test it directly.
Treatment
Treating H. pylori requires a combination of antibiotics taken alongside an acid-suppressing medication. A single antibiotic won’t work because resistance develops too quickly. The current standard recommended by the American College of Gastroenterology is a four-drug regimen taken for 14 days: an acid reducer, two different antibiotics, and a bismuth compound (the active ingredient in Pepto-Bismol). This combination is called bismuth quadruple therapy.
The older three-drug approach that relied on clarithromycin is no longer recommended as a first-line option unless lab testing confirms the bacterium is sensitive to it. That shift happened because clarithromycin resistance now exceeds 15% in most countries surveyed. Resistance to another commonly used antibiotic, levofloxacin, has climbed above 15% in over half the countries studied. Amoxicillin remains effective in most of the world, with resistance under 2% in nearly half the countries tracked, though parts of Africa are a notable exception with resistance rates above 90%.
Treatment typically eliminates the infection in the majority of patients on the first try. After finishing the course, your doctor will usually retest you (with a breath test or stool test) at least four weeks later to confirm the bacterium is gone. If the first round fails, a different combination of antibiotics is used for the second attempt.
Diet During and After Treatment
No specific diet can cure an H. pylori infection, but what you eat can make a real difference in how you feel while your stomach heals. Carbonated drinks distend the stomach, increasing pain and reflux. Alcohol directly worsens stomach inflammation and is best avoided entirely during treatment and while an ulcer is healing. Spicy and highly acidic foods don’t cause the infection, but they can aggravate an already inflamed stomach lining.
Probiotics have shown some benefit as an add-on during antibiotic treatment, primarily by reducing side effects like diarrhea and bloating. They don’t replace antibiotics and won’t clear the infection on their own, but they can make the two-week treatment course more tolerable.
Global Trends in Infection Rates
H. pylori prevalence has been declining for decades, driven largely by improved sanitation and living conditions. Global adult prevalence dropped from about 53% before 1990 to roughly 44% between 2015 and 2022, a reduction of nearly 16%. Significant declines have occurred across the Western Pacific, Southeast Asia, and Africa.
The picture is less encouraging for children. About 35% of children and adolescents worldwide still carry the infection, and that number has not significantly decreased in any world region. Since childhood is when most infections are acquired, the lack of progress in younger age groups suggests the overall burden will remain substantial for decades. No vaccine against H. pylori has yet achieved long-term effectiveness or regulatory approval, so prevention still comes down to basic hygiene: clean water, handwashing, and safe food handling.