Helicobacter pylori Is Common—but It Can Be Dangerous
Helicobacter pylori is a spiral-shaped bacterium that colonizes the lining of the human stomach and can cause chronic gastritis, peptic ulcers and stomach cancer.
It is an extremely common chronic infection, affecting nearly half the world’s population. In South Korea, an estimated 50 to 60 percent of people are infected.
Doctors once believed that bacteria could not survive in the stomach because of its powerful acid. That changed in 1982, when Australian doctors Barry Marshall and Robin Warren proved that the bacterium existed. They received the 2005 Nobel Prize in Physiology or Medicine for their work.
The International Agency for Research on Cancer (IARC), part of the World Health Organization (WHO), classified H. pylori in 1994 as a Group 1 carcinogen.
This article provides a detailed overview of H. pylori, including its biology, routes of transmission, associated diseases, and the latest approaches to diagnosis and treatment.
1. What Is H. pylori? Its Definition and Biological Characteristics
How It Survives in Stomach Acid
The human stomach secretes hydrochloric acid ($HCl$) to digest food and help keep pathogens out. As a result, the stomach maintains an extremely acidic pH of around 1 to 2, a hostile environment in which most bacteria die almost immediately. H. pylori, however, has several powerful survival mechanisms.
- Urease production: H. pylori breaks down urea in the stomach into ammonia and carbon dioxide. Because ammonia is alkaline, it neutralizes the strong acid around the bacterium, creating a kind of alkaline protective shield. This reaction is also the basis of the urea breath test (UBT), one of the standard diagnostic tests.
- Spiral shape and flagella: The bacterium has several flagella, or tail-like structures, at one end. These allow it to move through the stomach’s mucus layer and attach firmly to the surface of the cells. By settling deep within the mucosa, it avoids direct exposure to stomach acid.
- Toxin production: Depending on the strain, H. pylori can inject toxic proteins known as cytotoxin-associated gene A and vacuolating cytotoxin A. These toxins damage stomach-lining cells and trigger severe inflammation, promoting chronic gastrointestinal disease and cellular changes that can lead to cancer.
2. How H. pylori Spreads
Rather than living primarily in the natural environment, such as water or soil, H. pylori survives mainly in humans—especially in the gastrointestinal tract and saliva. Transmission generally occurs from person to person and is medically categorized as follows.
Oral-to-Oral Transmission
This route involves transmission through saliva. In South Korea and other parts of East Asia, shared dishes of soup, stews and side dishes are often eaten with individual spoons, and people may also share or pass around drinking glasses. These customs can contribute to a high rate of transmission among family members.
Chewing food before feeding it to a young child is another important potential source of infection. Casual kissing between adults is thought to carry a relatively low risk because the concentration of the bacterium in saliva is low, although transmission cannot be ruled out with prolonged close contact.
Fecal-to-Oral Transmission
In this route, material contaminated with an infected person’s stool enters another person’s mouth through the hands, food or drinking water.
It was more common in the past, when sanitation was poorer, and remains a concern in areas with inadequate water and sewage systems. Young children may become infected by putting contaminated hands in their mouths or by drinking polluted groundwater.
Key Features of the Infection
Most infections are acquired by the age of five.
New infections are uncommon in adulthood because the stomach’s immune defenses and protective barriers become more robust. In other words, H. pylori detected in adults was usually acquired during childhood and survived in the stomach for decades.
3. Diseases and Complications When the Infection Is Left Untreated
Not everyone infected with H. pylori experiences symptoms right away.
About 80 percent of infected people remain symptom-free carriers throughout their lives. But when the infection is left untreated for decades, ongoing damage to the stomach lining can gradually lead to the following serious diseases.
[Normal stomach lining] ──> [Acute/chronic gastritis] ──> [Atrophic gastritis] ──> [Gastric intestinal metaplasia] ──> [Gastric adenocarcinoma (stomach cancer)]
1) Chronic Gastritis
White blood cells continuously gather around areas colonized by the bacterium, releasing inflammatory cytokines. The process may begin as acute gastritis, then gradually spread throughout the stomach and become chronic.
On endoscopy, the stomach lining may appear rough and bumpy, like gooseflesh, or show nodules—a pattern known as nodular gastritis.
2) Atrophic Gastritis
When chronic inflammation continues for years or decades, the glandular cells in the stomach lining are destroyed, causing the lining to thin. This is known as atrophic gastritis, and it can sharply reduce stomach-acid production. People with atrophic gastritis face a stomach-cancer risk several times higher than that of people with a healthy stomach lining.
3) Gastric Intestinal Metaplasia
As atrophic gastritis progresses, stomach-lining cells may change into cells that resemble those found in the small or large intestine, apparently as an adaptation to survive in a chronically inflamed environment.
This condition is called gastric intestinal metaplasia and is considered a precancerous stage. Once it develops, eradicating H. pylori may not restore the stomach lining to normal, making regular endoscopic follow-up essential.
4) Peptic Ulcers: Gastric and Duodenal Ulcers
H. pylori weakens the stomach’s protective lining, allowing stomach acid to penetrate the tissue itself.
This can cause gastric and duodenal ulcers—deep sores that form when the lining breaks down. H. pylori is found in approximately 90 to 95 percent of people with duodenal ulcers and 70 to 80 percent of those with gastric ulcers.
Without eradication treatment, ulcers may keep returning even with medication. In severe cases, they can cause a perforated stomach wall or massive bleeding, both of which can be life-threatening.
5) Gastric Adenocarcinoma
People infected with H. pylori have a two- to sixfold higher risk of developing stomach cancer than those who are not infected.
Persistent inflammation, repeated cycles of cell destruction and regeneration, and toxin-induced DNA damage can combine to produce cancerous cells.
South Korea is one of the countries with the highest rates of stomach cancer worldwide, partly because salty and charred foods are common in the diet and genetic factors may also play a role. This makes careful management of H. pylori particularly important.
6) MALT Lymphoma
MALT lymphoma is a distinctive type of malignant tumor that develops in the lymphoid tissue of the stomach lining. Remarkably, in its early stages, MALT lymphoma may go into complete remission—and potentially be cured—with antibiotic treatment to eradicate H. pylori alone, without other cancer therapies.
7) Conditions Outside the Stomach: Unexplained Iron-Deficiency Anemia and Low Platelet Counts
By affecting stomach acidity and interfering with iron absorption, H. pylori may contribute to chronic iron-deficiency anemia.
In some cases, antibodies produced against the bacterium mistakenly attack the body’s own platelets, causing immune thrombocytopenic purpura (ITP).
4. How H. pylori Is Diagnosed
Tests for H. pylori generally fall into two categories: endoscopic tests and non-endoscopic tests.
Invasive Tests Using Endoscopy
- Rapid urease test (CLO test): During an upper endoscopy, a small sample of stomach tissue is placed in a urea-containing test kit. If H. pylori is present, its urease enzyme causes the kit to change color from yellow to red or pink. The test is fast and accurate, making it one of the most widely used clinical tests.
- Histopathological examination: A sample of the stomach lining is stained and examined under a microscope to identify the bacterium directly.
- Bacterial culture: The bacterium is grown from a tissue sample. This method is used mainly after treatment failure to determine which antibiotics the bacterium is resistant to through susceptibility testing.
Noninvasive Tests Without Endoscopy
- Urea breath test (UBT): The patient takes a special carbon-labeled urea pill, after which breath samples are collected and analyzed. If H. pylori is present, the proportion of carbon isotopes in the carbon dioxide exhaled rises. Because it is highly accurate and convenient, the test is the standard way to confirm that the bacterium has been fully eradicated after treatment.
- Serologic antibody test: A blood sample is analyzed for antibodies against H. pylori. Because antibodies may remain after a past infection has been successfully treated, a positive result does not necessarily indicate an active infection.
- Stool antigen test: This test detects fragments of H. pylori proteins, known as antigens, in stool. It can be useful for children and pregnant women who may have difficulty undergoing endoscopy or a breath test.
5. Current Treatments and Precautions
Unlike viral illnesses, H. pylori infection is treated with eradication therapy—a combination of a powerful acid-suppressing drug and several antibiotics.
Because H. pylori is a bacterium, it cannot be completely eliminated with probiotic drinks or dietary supplements alone. Prescription medication from a doctor is required.
In response to rising antibiotic resistance, recent international and South Korean clinical guidelines, including the 2025–2026 revisions, recommend the following stepwise treatment protocols.
1) First-Line Eradication Therapy
This is the standard combination a doctor typically prescribes first. Whereas treatment once lasted seven days, a 14-day course is now strongly recommended as the standard to improve efficacy in the face of antibiotic resistance.
Standard Triple Therapy
- Combination: Acid suppressant + amoxicillin + clarithromycin
- Key features: Once the long-standing standard, this regimen has become less reliable as clarithromycin resistance among South Koreans has risen sharply, exceeding 30 percent. When prescribed empirically without resistance testing, its eradication rate has fallen to around 70 percent.
- Tailored therapy: Doctors increasingly use PCR testing before treatment to determine whether the bacterium carries genes associated with clarithromycin resistance. Triple therapy is selected only when resistance is absent, producing eradication rates above 90 percent.
Bismuth Quadruple Therapy and Variations
- Combination: Acid suppressant + bismuth + metronidazole + tetracycline
- Key features: This regimen may be selected as a first-line option when clarithromycin resistance is suspected or confirmed by PCR, or when a high chance of success is desired from the outset. It involves more medications and a more complicated schedule, but is effective against resistant strains.
The Introduction of P-CABs
One of the biggest recent changes in eradication treatment is the increasing use of potassium-competitive acid blockers (P-CABs), such as tegoprazan and vonoprazan, instead of traditional proton pump inhibitors (PPIs).
Antibiotics work most effectively when the pH inside the stomach is closer to neutral—around 6 to 7.
P-CABs suppress stomach acid rapidly and powerfully from the first day, maintaining the desired pH and substantially improving the antibiotics’ ability to eradicate the bacterium.
2) Second- and Third-Line Salvage Therapy
If a follow-up urea breath test shows that H. pylori remains after the patient has completed a two-week first-line course, which succeeds in approximately 70 to 80 percent of cases, doctors switch to a salvage regimen using different antibiotics. When triple therapy was used initially, the second-line treatment is typically bismuth quadruple therapy. If that also fails, a third-line regimen may involve levofloxacin-based triple therapy or rifabutin.
3) Side Effects and How to Manage Them
Because eradication regimens contain several antibiotics, often at high doses, about 20 to 30 percent of patients experience side effects.
- Common symptoms: A bitter or metallic taste, severe diarrhea or loose stools, nausea, abdominal pain, indigestion and dizziness.
- Important precautions: Skipping doses or stopping treatment early because of side effects may allow the bacterium to survive while promoting strong antibiotic resistance, making subsequent treatment much more difficult. If symptoms are severe, patients should consult their doctor about adjusting the regimen or adding a probiotic. Whenever possible, the full prescribed course should be completed.
6. Prevention and Lifestyle Measures
Even after a negative follow-up urea breath test confirms successful treatment, reinfection remains possible if everyday precautions are neglected.
Fortunately, the annual reinfection rate among adults is relatively low—less than 2 to 4 percent—but preventive measures are still important, especially to reduce the risk of transmission within families.
- Use individual plates: Serve soup, stews and side dishes onto each person’s own plate rather than eating directly from shared dishes.
- Do not share drinking glasses: Passing glasses around at social gatherings can facilitate transmission through saliva and should be avoided.
- Practice careful hygiene: Wash your hands thoroughly with soap and running water after using the bathroom and before eating. Never chew food and feed it to an infant or young child.
- Have regular checkups: People diagnosed with atrophic gastritis or gastric intestinal metaplasia should continue to receive an upper endoscopy every one to two years after eradication treatment to monitor changes in the stomach lining and check for cancer.
7. Summary
H. pylori is a specialized bacterium capable of surviving in the stomach’s highly acidic environment. If left untreated, it can progress from chronic gastritis to peptic ulcers and gastric intestinal metaplasia and ultimately become a clear carcinogenic cause of stomach cancer.
Fortunately, advances in medicine—including newer drugs such as P-CABs and personalized eradication therapy guided by PCR testing—mean that most infections can be safely cured with two weeks of properly taken medication. If heartburn or chronic indigestion persists, or if an endoscopy shows signs of inflammation, consult a specialist about H. pylori testing. If the infection is confirmed, prompt treatment is one of the most reliable ways to protect stomach health and reduce the risk of stomach cancer.
Frequently Asked Questions
Does every H. pylori infection need to be treated?
Not every infected person necessarily requires treatment. However, eradication therapy is strongly recommended for people with gastric or duodenal ulcers, those who have undergone treatment for early stomach cancer, people with MALT lymphoma, those with atrophic gastritis or gastric intestinal metaplasia, and people with a family history of stomach cancer. As evidence of its cancer-prevention benefits has grown, the number of people considered candidates for treatment has gradually expanded. A specialist should determine whether treatment is appropriate based on the endoscopy findings and the individual’s risk factors.
Can H. pylori eradication completely prevent stomach cancer?
Eradication treatment significantly lowers the risk of stomach cancer, but it does not eliminate it entirely. When atrophic gastritis or gastric intestinal metaplasia has already developed, some cancer risk remains even after eradication, so regular endoscopic surveillance is still necessary. Treatment is most effective at preventing cancer when it is given before extensive damage to the stomach lining occurs.
Does H. pylori spread easily among family members?
H. pylori is often transmitted among family members. Many people become infected during childhood through close contact with parents or siblings, and sharing soup, stews or spoons can increase the risk. New infections in adulthood are relatively uncommon, and the reinfection rate after treatment is also low—less than 2 to 4 percent per year.
Can I drink alcohol during H. pylori eradication treatment?
It is not recommended. In particular, drinking alcohol while taking a regimen containing metronidazole can cause a severe disulfiram-like reaction, including vomiting, headaches, facial flushing and a pounding heartbeat. Alcohol can also irritate the stomach lining and reduce treatment effectiveness. The safest approach is to avoid alcohol throughout treatment and for several days afterward.
Can probiotics or dietary supplements eliminate H. pylori?
No. There is currently no evidence that probiotics or dietary supplements alone can completely eliminate H. pylori. Some probiotics may help reduce antibiotic-related side effects such as diarrhea and abdominal pain and may modestly improve eradication rates, but eliminating the bacterium requires treatment with an acid suppressant and antibiotics. Probiotics are supportive therapy only; they cannot replace antibiotics.
