Helicobacter pylori is a spiral-shaped bacterium that lives in the lining of the human stomach. Roughly 44% of adults worldwide carry it, making it one of the most common chronic infections on the planet. Most people never realize they’re infected, but in a significant minority, H. pylori triggers stomach ulcers, chronic inflammation, and a sharply increased risk of stomach cancer.
How It Survives in Your Stomach
The stomach is one of the harshest environments in the body, with acid strong enough to break down food. Most bacteria can’t survive there. H. pylori can, thanks to two key adaptations.
First, its corkscrew shape lets it burrow through the thick layer of mucus that coats the stomach wall. Once it reaches the tissue underneath, the environment is less acidic and more hospitable. Second, H. pylori produces an enzyme that splits urea (a natural compound in the stomach) into ammonia and carbon dioxide. The ammonia neutralizes the acid in the bacterium’s immediate surroundings, creating a small protective buffer zone. When conditions turn harsh, H. pylori can also shift into a dormant, ball-shaped form that resists environmental stress, then revert to its active spiral form when conditions improve.
How It Spreads
H. pylori passes from person to person, most likely through the mouth or through contact with contaminated water or food. Researchers have identified three overlapping routes: mouth-to-mouth (through saliva), stomach-to-mouth (through reflux or vomiting), and fecal-to-mouth (through water or food contaminated with sewage). These routes aren’t mutually exclusive and probably all play a role.
Most infections are acquired in childhood, often within families. In regions with limited sanitation infrastructure, contaminated water is a significant source. Humans and animals act as long-term carriers, shedding the bacterium into water supplies where it survives long enough to infect the next person. This helps explain why infection rates are higher in lower-income countries and why improving water quality has coincided with falling infection rates globally. The worldwide prevalence dropped from about 53% before 1990 to 44% in recent years among adults, though it remains around 35% in children and adolescents.
Symptoms Most People Experience
The majority of people with H. pylori have no symptoms at all. The infection can persist for decades without causing noticeable problems. When symptoms do appear, they’re usually tied to gastritis (inflammation of the stomach lining) or a peptic ulcer. Common signs include:
- A burning or aching pain in the upper abdomen, often worse on an empty stomach
- Bloating and frequent burping
- Nausea or loss of appetite
- Unintended weight loss
These symptoms overlap with many other digestive conditions, so they don’t point to H. pylori on their own. The pain pattern is the most distinctive clue: a gnawing discomfort that flares when you haven’t eaten and eases after a meal or an antacid.
Ulcers and Stomach Cancer
H. pylori is the dominant cause of peptic ulcers. In the years after the bacterium was first identified, studies found that 95% of duodenal ulcers and 85% of gastric ulcers were linked to H. pylori infection. People carrying the bacterium are 3 to 10 times more likely to develop an ulcer over their lifetime compared to those without it.
The cancer connection is equally striking. The World Health Organization classifies H. pylori as a Group 1 carcinogen, meaning there is sufficient evidence it causes cancer in humans. A large simulation study using Japanese cancer registry data estimated that infected men face a 17% lifetime risk of developing stomach cancer by age 85, compared to just 1% for uninfected men. For women, the numbers were about 8% versus 0.5%. Some cohort studies have found relative risks exceeding 15 to 20 times higher in infected individuals. H. pylori is also linked to a rare type of stomach lymphoma.
These numbers don’t mean every infected person will develop cancer. Most won’t. But chronic, untreated infection sustained over decades is the single biggest risk factor for stomach cancer worldwide.
How It’s Diagnosed
If your doctor suspects H. pylori, there are several ways to test for it, and the noninvasive options are just as accurate as the invasive ones in most situations.
The urea breath test is the most commonly used noninvasive method. You swallow a small amount of a specially labeled urea compound. If H. pylori is present in your stomach, the bacterium’s enzyme breaks it down, and you exhale a detectable byproduct. The test takes about 15 to 20 minutes. A stool antigen test works differently, detecting H. pylori proteins in a stool sample, and is similarly reliable. Blood antibody tests can confirm past exposure but can’t distinguish between a current and a previous infection, making them less useful for follow-up.
For people with more severe symptoms or warning signs, an endoscopy allows the doctor to look directly at the stomach lining and take small tissue samples. These biopsies can be tested for the bacterium and also checked for signs of ulceration or precancerous changes. But for straightforward diagnosis in an otherwise healthy person, the breath test or stool test is usually sufficient.
Treatment and Antibiotic Resistance
H. pylori is treated with a combination of antibiotics and an acid-reducing medication, taken together for 14 days. The current recommended first-line approach, according to the American College of Gastroenterology, is a four-drug regimen that includes an acid reducer, two antibiotics, and a bismuth compound (the active ingredient in Pepto-Bismol). This combination attacks the bacterium from multiple angles while reducing stomach acid to help the stomach lining heal.
For years, a simpler three-drug regimen using the antibiotic clarithromycin was the standard approach. That’s no longer recommended unless testing confirms the specific strain is susceptible. The reason: antibiotic resistance has become a serious problem. The World Health Organization classified clarithromycin-resistant H. pylori as a “high-priority” pathogen in 2017. Among patients who have already failed one round of treatment, clarithromycin resistance rates climb to roughly 76%, and they rise further with each subsequent failed attempt, reaching above 90% after three or more courses.
Resistance to other commonly used antibiotics follows the same pattern. Each failed treatment round selects for tougher, more resistant bacteria. This is why getting the first treatment right matters so much. When doctors can tailor the antibiotic choice based on sensitivity testing of the specific strain, cure rates stay high even in patients who have failed previous treatments. Alternative regimens exist for difficult cases, but the simplest path is an effective first attempt with an appropriate combination.
After completing treatment, your doctor will typically retest you (usually with a breath test or stool test) to confirm the infection has been cleared. This step is important because incomplete eradication can lead to recurrence and further resistance.