The short answer
H. pylori is a common stomach bacterium classified as a Group 1 carcinogen. Most infected people never get stomach cancer, but eradication roughly halves that risk.
IARC classified H. pylori as a Group 1 carcinogen in 1994 — strong evidence it can cause cancer in humans, not a statement that the risk for any one person is large.
About two-thirds of the world's population carries H. pylori, and United States prevalence varies widely by background, from roughly 21 percent to over 60 percent in different groups.
Most people with H. pylori never develop stomach cancer; stomach cancer accounts for about 1.5 percent of new United States cancers, an estimated 31,510 cases in 2026.
In a randomised trial in China, two weeks of eradication therapy cut gastric cancer incidence by about half over more than two decades of follow-up.
Watch: The stomach bacterium linked to cancer
54 sec · Captioned · H. pylori is a stomach cancer risk you can test for and treat with antibiotics.
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The full explanation.
A common infection with an uncommon consequence
Helicobacter pylori is a bacterium that lives in the stomach lining. About two-thirds of the world carries it. Most people pick it up as a child. Most never feel a thing. In the United States, how common it is depends a lot on background. One national survey found about 21 percent of non-Hispanic White adults had it. It found 52 percent of non-Hispanic Black adults and 64 percent of Mexican American adults.
In 1994 IARC classified H. pylori as a Group 1 carcinogen. Group 1 means the evidence that something can cause cancer in humans is strong. It says how sure the science is. It does not say how big the risk is. Both parts matter here. The link is real and solid. The risk to any one person is still small.
Stomach cancer makes up about 1.5 percent of new cancers in the United States. The American Cancer Society projects about 31,510 new cases and 10,740 deaths there in 2026. Now set that against two-thirds of the world carrying the bacterium. The maths is clear. Almost everyone who carries it never gets stomach cancer. For those infected, lifetime risk is usually put in the low single digits. It shifts with region, bacterial strain, family history, salt intake, and smoking.
Why this one is worth acting on anyway
Most cancer risk factors on this site are things you can reduce. This one you may be able to remove.
A randomised trial in Shandong, China gave people two weeks of antibiotics. It then followed them for more than twenty years. New stomach cancers fell by roughly half. A second trial looked at people who had surgery for an early stomach cancer. Clearing the bacterium halved the rate of a new, second stomach cancer. Gastric MALT lymphoma is a slow-growing lymphoma of the stomach lining. Nearly all of it is tied to H. pylori. Clearing the infection alone shrinks the tumor in most patients.
Few steps in cancer prevention look like that. A two-week course. A clear target. Randomised proof of benefit.
Who is tested
There is no national screening program in the United States. Testing everyone is not thought to be worth it, because stomach cancer is uncommon here. Instead, guidelines name the groups who should be tested and treated:
- People with a current or past stomach or duodenal ulcer.
- People who have had an early stomach cancer removed.
- People with gastric MALT lymphoma.
- People found to have atrophic gastritis (a thinned, inflamed stomach lining) or intestinal metaplasia.
- First-degree relatives of someone with stomach cancer.
- People who live with someone who has the infection.
Unexplained iron deficiency anemia and immune thrombocytopenia are also good reasons to test. If you fall into one of these groups, testing is a concrete request you can make.
How testing works
The urea breath test and the stool antigen test both pick up active infection. They are the usual choices when you are not having an endoscopy. A biopsy at upper endoscopy is used when you are having one anyway. Blood antibody tests are a poor choice here. Antibodies can linger for years after the bacterium is gone. So a positive result cannot tell a current infection from an old one.
How you prepare matters. Proton pump inhibitors can knock the bacterium back. So can recent antibiotics or bismuth. Either can give a false negative. Ask how to prepare. Do not change anything on your own.
After treatment
Antibiotic resistance has changed the picture. The 2024 American College of Gastroenterology guideline dropped the old clarithromycin-based triple therapy as a first choice. It now favours an optimised fourteen-day bismuth-based quadruple regimen. Which one suits you depends on your allergies, past antibiotic use, and local resistance patterns. That is a decision for your clinician.
One step often gets missed. Someone has to check that the bacterium is actually gone. Guidelines advise a breath test, stool antigen test, or biopsy. It should come at least four weeks after the antibiotics finish, with acid suppression paused first. Ask when yours is booked.
Did endoscopy show atrophic gastritis or intestinal metaplasia? If so, some risk remains even after the bacterium is cleared. Your clinician may advise regular endoscopic checks. Ongoing indigestion, trouble swallowing, vomiting, unplanned weight loss, or black stools need prompt review. That holds whatever your test results say.
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Words to know
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Common questions
I have H. pylori. What is my actual chance of getting stomach cancer?
For most people in the United States it is low. Stomach cancer makes up about 1.5 percent of new cancers nationally, and the large majority of the two-thirds of the world's population carrying H. pylori never develop it. Estimates for lifetime gastric cancer risk among infected people generally fall in the low single-digit percentages, and vary considerably by region, bacterial strain, family history, and diet.
Which test should I ask about?
The urea breath test and the stool antigen test both detect current, active infection and are the usual choices outside endoscopy. Biopsy during an upper endoscopy is another option if you are having one for other reasons. Blood antibody tests can stay positive for years after the infection has gone, so they cannot confirm active infection or cure. Preparation matters: acid-suppressing medicines and recent antibiotics can produce false negatives, so ask your clinician how to prepare.
Does treatment work, and how would I know?
Current regimens clear the infection in most people, though antibiotic resistance has reduced the effectiveness of some older combinations. The 2024 American College of Gastroenterology guideline recommends confirming eradication after treatment, using a breath test, stool antigen test, or biopsy, at least four weeks after finishing antibiotics. Confirmation is not automatic — it is reasonable to ask whether it has been arranged.
Should my family be tested too?
Infection often clusters in households, and guidelines now suggest testing household members of people found to have H. pylori, as well as first-degree relatives of people diagnosed with gastric cancer. Whether that applies to your family is a specific conversation to have with your clinician.
If I clear the infection, is my risk gone?
It is reduced, not erased — and how much depends on what damage was already present. Once atrophic gastritis or intestinal metaplasia has developed in the stomach lining, some elevated risk persists after eradication, and your clinician may recommend periodic endoscopic surveillance.
Questions to ask your doctor
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Written by: Cancer ExplainedSources last checked: 2026-08-13 what this meansLast updated: 2026-08-18Next planned review: 2027-07-30
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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