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H. pylori · a cause of cancer you can clear
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In one pass Stomach acid kills almost every bacterium swallowed with food.
Educational content, not medical advice — consult a clinician.
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Chapter 1
How it survives the acid
Stomach acid kills almost every bacterium swallowed with food. H. pylori survives not because it can withstand acid, but because it never touches the acid.
It carries an enzyme that splits urea, called urease. Urease breaks nearby urea down into ammonia and builds a local cloud of alkali. A small gate on the bacterium's surface lets only urea through, and it opens only as acid closes in. Once the mucus turns from gel to fluid, the bacterium swims under it onto the surface of the stomach-wall cells, where conditions are close to neutral.
This survival kit later became the way to find it: the common breath test measures exactly this urease activity.
It carries an enzyme that splits urea, called urease. Urease breaks nearby urea down into ammonia and builds a local cloud of alkali. A small gate on the bacterium's surface lets only urea through, and it opens only as acid closes in. Once the mucus turns from gel to fluid, the bacterium swims under it onto the surface of the stomach-wall cells, where conditions are close to neutral.
This survival kit later became the way to find it: the common breath test measures exactly this urease activity.
Mechanism · How it avoids the acid
Its full name is *Helicobacter pylori* (usually shortened to H. pylori). It carries one piece of equipment: urease, an enzyme that splits urea. Gastric juice already contains a little urea, and urease splits it into ammonia and carbon dioxide. Ammonia is alkaline, so it neutralizes, on the spot, the acid seeping in around the bacterium — in effect a cloud of alkali wrapped around itself (Scott 2002).The device even has a power-saving switch. A small gate on the bacterial surface lets only urea through. It normally stays shut and opens only as acid closes in, so no effort is wasted when there is no acid.
But the bacterium still has to leave the strong acid of the stomach cavity. A layer of mucus covers the stomach wall, thick as gel. It was long assumed that the corkscrew body screwed its way in, but the mechanism seen in experiments is neater: urease first raises the pH nearby, the mucus turns from gel to fluid, and the bacterium then swims through on its flagella (Celli 2009).
Under the mucus, it settles on the surface of the stomach's own cells. The pH there is close to neutral — the only mild spot in the stomach. So it does not live *in* the acid; it lives underneath it.
For how stomach acid is made and how the mucus barrier works, see Digestive System.
Numbers · Why the stomach holds so few bacteria
Since strong acid kills bacteria, the stomach was never home to many. A gram of stomach contents holds roughly 10¹ to 10³ bacteria; a gram of colon contents holds 10¹¹ to 10¹² (Liu 2024). That is about a billion-fold difference.This contrast answers a widespread worry: whether eradication treatment wrecks the stomach's good bacteria. It comes back in the chapter What eradication does and doesn't do.
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Chapter 2
The decades-long road to cancer
H. pylori does not become gastric cancer overnight. It walks a road that takes decades: gastritis, atrophy, intestinal metaplasia, dysplasia, and only then cancer. The first half of that road can be walked back.
What matters is not the names of the stops but time and direction: the further along, the harder it is to turn back. So the honest statement is not that a later stop is hopeless. It is that the earlier eradication happens, the more certain the benefit.
And do not read the road as a verdict: the vast majority of infected people stay at the first stop for life and never reach gastric cancer.
What matters is not the names of the stops but time and direction: the further along, the harder it is to turn back. So the honest statement is not that a later stop is hopeless. It is that the earlier eradication happens, the more certain the benefit.
And do not read the road as a verdict: the vast majority of infected people stay at the first stop for life and never reach gastric cancer.
Mechanism · Five stops from gastritis to cancer
The pathologist Correa mapped this road, and it now carries his name: the Correa cascade (Correa 1992; Correa & Piazuelo 2012):Chronic gastritis — the bacterium moves in and the stomach wall stays inflamed for years. The vast majority of people stop here for life and feel nothing.Atrophic gastritis — the inflammation burns too long, part of the glands that make acid and digestive enzymes is worn away, and the wall thins.Intestinal metaplasia — stomach-lining cells are replaced by cells that look like intestine. The stomach grows intestine in the wrong place.Dysplasia — cells start growing out of order.Gastric cancer.
The first two stops are clearly reversible: after eradication, both chronic gastritis and atrophy improve noticeably (Liang 2024 , atrophy 2.96; OR is the odds ratio, and above 1 means improvement was more common in the eradication group). Intestinal metaplasia has traditionally been called the point of no return, but that is now contested. The same meta-analysis found that early metaplasia also improves after eradication (OR 2.41), while other evidence suggests that for people already at metaplasia or dysplasia, eradication buys a smaller drop in cancer risk.
So metaplasia does not mean it is hopeless; it means that the further along, the less eradication can win back. That is exactly why guidelines keep stressing that the infection should be dealt with before precancerous changes appear (Kyoto 2015).
Evidence · How many infected people got cancer
Being infected with H. pylori does not mean you will get gastric cancer. A long-term Japanese follow-up study puts numbers on it (the participants were patients seen at a hospital for digestive complaints): of 1,246 infected people followed for an average of 7.8 years, 2.9% developed gastric cancer; among 280 uninfected people, not one did (Uemura 2001).Read it in both directions. The vast majority of infected people did not reach gastric cancer, so a positive test is not a death sentence. But the uninfected group had no cases at all, and that contrast shows the risk from infection is real. Keep in mind, too, that this is a rate among patients, and it cannot be applied directly to people in the general population without symptoms.
What makes this worth taking seriously is another trait: among known causes of cancer, it is one of the few that a single course of treatment can remove.
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Chapter 3
How a bacterial protein enters cells
Two people, the same infection: one is fine for life, the other reaches gastric cancer. Whether the strain carries a protein called CagA is one of the most important forks between them.
Once a virulent strain attaches to a stomach-wall cell, it extends a fine tube and injects CagA into the cell like a syringe. The host's own enzymes tag CagA with a phosphate, and it becomes an adaptor that grabs the host's signaling proteins: the cell loses track of up and down, and it is pushed to keep dividing. The type common in East Asia grips more tightly.
For now, this layer does not change what you should do: if infection is found, eradication is recommended, whatever the strain.
Once a virulent strain attaches to a stomach-wall cell, it extends a fine tube and injects CagA into the cell like a syringe. The host's own enzymes tag CagA with a phosphate, and it becomes an adaptor that grabs the host's signaling proteins: the cell loses track of up and down, and it is pushed to keep dividing. The type common in East Asia grips more tightly.
For now, this layer does not change what you should do: if infection is found, eradication is recommended, whatever the strain.
Mechanism · How CagA gets injected into cells
Once a virulent strain attaches to a stomach cell, it extends an extremely fine tube, formally called a type IV secretion system. What it does is act like a syringe: it punctures the cell and injects CagA straight in (Hatakeyama 2004).Inside, CagA starts making trouble. The host's own enzymes tag it with phosphate, and the tagged CagA becomes an adaptor that grabs the host's signaling proteins. The captured circuits scramble, with two consequences: the cell loses track of up and down (its polarity breaks), and it gets pushed to keep dividing.
More to the point, there is more than one CagA. Its tail carries a repeated sequence, and by that sequence it splits into an East Asian type and a Western type. The East Asian segment grips host signaling proteins more tightly (Ji 2024). By the mechanism, a tighter grip pushes the downstream signal harder, and the risk of malignant change rises with it.
Strains circulating in East Asia more often carry the more virulent type. That is part of the molecular explanation for East Asia's high gastric cancer rate. Only part: diet, salt, genetics, and screening intensity all play a role. And the evidence for this layer comes mostly from cell and structural experiments, not from population trials.
Clinical · Do you need strain typing?
Now that you know about CagA, should you ask for an extra strain-typing test? No need, for now.The guideline position is blunt: everyone who is infected should be offered eradication, whatever the strain, because for an individual the action is the same either way (Maastricht VI 2022). Typing is currently a research and epidemiology tool, not a fork in clinical decisions.
So this layer is not here to add a test. It is here so you understand why East Asia cares so much about this infection, and why the same bacterium adds up differently in different places.
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Chapter 4
Why China carries the load
About one in two people in China carries H. pylori. It travels mouth-to-mouth and by the fecal-oral route, and its main site of transmission is the dining table: shared dishes, no serving chopsticks, elders chewing food before feeding a child. So whole households often end up infected.
What needs to change is how people eat, not who they are. Serving chopsticks and spoons, and not pre-chewing food for a child, are enough. There is no need to set aside an infected person's bowl and chopsticks, and certainly no reason to move anyone away from the table.
Hepatitis B is the counterexample: it is not spread by eating together, so setting aside dishes for people with hepatitis B was only ever discrimination.
What needs to change is how people eat, not who they are. Serving chopsticks and spoons, and not pre-chewing food for a child, are enough. There is no need to set aside an infected person's bowl and chopsticks, and certainly no reason to move anyone away from the table.
Hepatitis B is the counterexample: it is not spread by eating together, so setting aside dishes for people with hepatitis B was only ever discrimination.
In practice · What to change at the table
It spreads mouth-to-mouth and by the fecal-oral route, and transmission within the household is among the chief sources (Zhou 2023 national family survey). Chinese eating habits happen to pave that road flat:Communal dishes — everyone's chopsticks take turns in the same plate.No serving chopsticks — your chopsticks, wet with saliva, go back into shared food.Elders chewing food before feeding a child — the most direct mouth-to-mouth channel.
The result is infection by the household. This survey, covering 10,735 families across 29 provinces, found that on average 71% of households had at least one infected member (Zhou 2023).
The Chinese consensus on family-based control gives plain steps: serving chopsticks and spoons, individual portions, and no pre-chewed food for children (Ding 2022). They target exactly the three channels above, and none of them requires isolating anyone.
A counterexample helps calibrate the fear. Hepatitis B was misunderstood in China for decades, and countless people were shut out because of it. Yet hepatitis B is precisely not spread by eating together or sharing utensils (CDC); it travels by blood, sexual contact, and from mother to child. The two spread in entirely different ways. H. pylori really does move along the dining table, so serving chopsticks help; hepatitis B does not, so segregating someone's dishes was only ever discrimination. For that thread, see Hepatitis B.
Put the conclusion the other way round: serving chopsticks for H. pylori, common sense for hepatitis B. Neither requires isolating a person.
Numbers · Infection rate and cancer burden
Infection rate: a pooling 412 studies and 1.37 million people put mainland China's combined infection rate at 44.2% (95% 43.0–45.5, meaning the true value very likely falls in that range), which implies about 589 million people infected (Ren 2022). Data from the past decade show a slow decline, but the order of magnitude has not changed.Cancer burden: China had roughly 479,000 new gastric cancers and 373,000 gastric cancer deaths in 2020, more than 40% of the global burden (Yin 2025).
A high infection rate is not the only reason gastric cancer runs high, but it is the largest one, and the only one that can be removed. Another accomplice is high-salt preserved food; that correlational debate is unpacked in Kimchi, so it is not repeated here.
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Chapter 5
How it's found · how it's treated
The most common way to find it is to breathe into a tube. You drink a small cup of labeled urea; if the bacterium is in your stomach, its urease splits the urea as usual, and labeled carbon dioxide comes out of your lungs. The test measures not the bacterium itself but the activity of its survival kit.
So any drug that damps that activity can push the result toward a false negative. Which drugs to stop before testing, and how long to wait before retesting, should follow your doctor's instructions.
Treatment is a medical decision. China's first-line regimen became a more complex combination because of resistance: this is not "more drugs is better", it is the choice left after resistance broke the simpler regimen.
So any drug that damps that activity can push the result toward a false negative. Which drugs to stop before testing, and how long to wait before retesting, should follow your doctor's instructions.
Treatment is a medical decision. China's first-line regimen became a more complex combination because of resistance: this is not "more drugs is better", it is the choice left after resistance broke the simpler regimen.
Clinical · How it is found and treated
The breath test works precisely because the bacterium's survival kit (urease) gives it away. The logic is clean:1. You drink a small cup of water in which the urea has been swapped for a labeled version (carbon-13 or carbon-14).
2. If H. pylori is in your stomach, its urease splits that urea as usual, and the carbon dioxide released carries the label.
3. The labeled carbon dioxide enters the blood, reaches the lungs, and you breathe it out.
4. The machine reads your breath: label present means bacteria present; no label means none.
In other words, it does not measure the bacterium; it measures urease activity. The very kit that keeps it alive in acid is the signature it cannot hide. Accuracy is good enough: in a , sensitivity was about 96% (about 96% of people who carry the bacterium test positive) and specificity about 93% (about 93% of people who do not carry it test negative) (Ferwana 2015).
For treatment, China's first-line regimen is bismuth quadruple therapy for 14 days (2022 Chinese guideline): an acid-suppressing drug, a proton-pump inhibitor (), plus bismuth, plus two antibiotics, taken for 14 days.
Why not the simpler triple therapy? Because antibiotic resistance broke it. Resistance rates in China: clarithromycin 30.7%, metronidazole 70.1%, levofloxacin 33.0% (Zeng 2024). At those levels, clarithromycin-based standard triple therapy is no longer reliable. Meanwhile amoxicillin (2.4%) and tetracycline (2.5%) resistance has stayed low and stable. Bismuth quadruple therapy stands on those two intact pillars plus bismuth's own antibacterial action. This is not more drugs is better; it is a choice that resistance forced.
For the pros and cons of long-term PPI use, see .
In practice · Two traps: before testing, and retesting
Before testing: the breath test reads urease activity, so any drug that suppresses the bacterium's activity pushes the result toward a false negative. Proton-pump inhibitors (), antibiotics, and bismuth all count. How long to stop them beforehand is your doctor's call; do not take a PPI and go blow into the tube.Retesting: finishing the course does not mean eradication succeeded, so you must retest. And not right away: just after the drugs stop, the bacteria may only be suppressed rather than cleared, and testing then also reads as a false negative. The consensus definition: still undetectable 4 to 6 weeks after treatment ends (Maastricht VI 2022).
Both traps are the same trap. The breath test measures activity, not presence. Suppress the activity and the test goes blind.
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Clinical · Does a positive test mean endoscopy now?
Not necessarily. Whether to have an endoscopy, and how often, depends on your age, family history, and symptoms, and on the extent and stage of changes already in your stomach. That is a doctor's judgment, not something a positive result sets off automatically.The European guideline tiers it. People who already have extensive atrophy or intestinal metaplasia need scheduled, high-quality endoscopic surveillance. People with mild changes confined to the antrum (the outlet section of the stomach) and no other risk factors are not advised to have routine surveillance (MAPS III 2025).
One situation does not wait for anyone's schedule, though. If alarm symptoms appear — trouble swallowing, vomiting blood or black stools, unexplained weight loss, persistent vomiting, anemia — please see a doctor now; do not search online.
Chapter 6
What eradication does and doesn't do
Clearing H. pylori lowers gastric cancer risk, but it does not bring it to zero. In healthy infected people without precancerous changes, eradication roughly halves the rate of gastric cancer. But if the stomach has already reached atrophy or intestinal metaplasia, those structural changes do not vanish because the bacterium was cleared. Removing the cause is not the same as erasing the road already walked.
The International Agency for Research on Cancer (IARC) classifies it as a Group 1 carcinogen. That means the evidence that it causes cancer is conclusive, not that it is as dangerous as tobacco. What makes it genuinely special: among known causes of cancer, it is one of the few that a single course of treatment can remove.
The International Agency for Research on Cancer (IARC) classifies it as a Group 1 carcinogen. That means the evidence that it causes cancer is conclusive, not that it is as dangerous as tobacco. What makes it genuinely special: among known causes of cancer, it is one of the few that a single course of treatment can remove.
Evidence · How much eradication lowers risk
The lowering first. In healthy infected people without precancerous changes, eradication cuts the rate of gastric cancer to about half (, RR 0.54), and gastric cancer deaths fall with it (RR 0.61). In more concrete terms: treat about 72 people to prevent 1 gastric cancer (Ford 2020, a of randomized trials).The higher the risk, the clearer the benefit. A Korean double-blind, placebo-controlled randomized trial recruited people with a first-degree relative who had gastric cancer (a parent or sibling) and followed them for about 9.2 years: 1.2% of the eradication group developed gastric cancer versus 2.7% on placebo, and among those whose infection was actually cleared, risk fell by more than 70% (Choi 2020).
Now the not-zero part. People who have already reached atrophy or intestinal metaplasia still carry residual risk, so the endoscopic surveillance they need still applies, at intervals a doctor sets from the actual extent and stage in their stomach (MAPS III 2025).
IARC placed it in Group 1 in 1994. Group 1 describes how conclusive the evidence is, not how large the danger is; headlines routinely swallow that distinction. You cannot take back the cigarettes you smoked, but you can show this bacterium the door.
IARC now recommends making screen-and-treat a public health priority in regions and populations where gastric cancer runs high (IARC 2025). China is exactly such a place.
Myth · Bad breath, garlic, and probiotics
Bad breath means H. pylori? No. Eighty to ninety percent of bad breath comes from the mouth itself: tongue coating, gum disease, oral hygiene (Memon 2023 systematic review). Seeing a dentist first makes far more sense than a breath test first.Garlic or honey can kill it? No. Garlic inhibits it beautifully in a test tube, but tested in actual people it had no effect at all (Graham 1999). This is the textbook lesson that working in a test tube is not working in the body: your stomach never reaches that test-tube concentration, and the bacteria are hiding under the mucus anyway.
Probiotics can kill it? No again. Their real role is supportive: added to a proper regimen, they raised the eradication rate by only about a tenth in relative terms ( 1.12), and their main benefit is fewer side effects during treatment (Lv 2015 ). Useful, but no substitute for antibiotics.
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Myth · Wrecked flora, and no symptoms, no problem
Eradication wrecks the stomach's good bacteria? This treats the stomach as if it were the colon. The numbers from the chapter How it survives the acid earn their keep here: the stomach holds only 10¹ to 10³ bacteria per gram, the colon 10¹¹ to 10¹² (Liu 2024), about a billion-fold difference. The acid is too strong; the stomach was never a thriving microbial community, so there is no good flora there waiting to be wrecked. The disturbance that antibiotics cause to the gut flora during treatment is real. It is mostly short-term and largely recovers afterward, though not always completely. And the organism being shown the door is a Group 1 carcinogen.No symptoms, no problem? This is the one to watch, because the first half of the Correa cascade has no symptoms by nature. Chronic gastritis, atrophy, metaplasia: most of the time you feel nothing, and by the time you do, the road is often long behind you. Hence the guideline position: a positive test warrants eradication, symptoms or not (Maastricht VI 2022).
But do not read that as panic. Go back to the Uemura 2001 numbers: among infected patients, 2.9% developed gastric cancer over 7.8 years, and the vast majority did not. This is worth doing not because it is frightening, but because it is cheap, well-defined, and finished once it is done.
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Safety · Which decisions belong to a doctor
This story is education about mechanism, not medical advice. Whether to test, whether to treat, which regimen, whether to have an endoscopy: let a doctor decide from your actual situation. That goes especially for the regimen, since the resistance picture differs by region and shifts over time.If alarm symptoms appear — trouble swallowing, vomiting blood or black stools, unexplained weight loss, persistent vomiting, anemia — do not search online; see a doctor now.
To keep reading: for how stomach acid and the mucus barrier work, see Digestive System; for the pros and cons of long-term use, see ; for the correlational debate about high-salt preserved food and gastric cancer, see Kimchi; for how food as a whole shifts the odds of cancer, see the story on diet and cancer risk.
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