Most people infected with H. pylori have no symptoms at all. The bacterium lives in the stomach lining of roughly half the world’s population, and the majority never know it’s there. But when symptoms do appear, they typically center on the upper abdomen: a gnawing or burning pain, bloating, nausea, and a loss of appetite that can gradually lead to weight loss.
Why Most Infections Stay Silent
H. pylori is remarkably common. In a large U.S. population-based study, almost two-thirds of asymptomatic patients tested positive for the bacteria, and a separate meta-analysis of over 1.7 million U.S. adults found an overall prevalence of about 17.6%. Rates vary by background: seroprevalence was highest among individuals born in Central America (75.1%) and lowest among non-Hispanic white individuals (45%).
The bacterium can persist for decades without causing noticeable problems. It survives the extreme acidity of the stomach by producing an enzyme that converts urea into ammonia, raising the pH in a thin layer around the bacterial cell. This lets it swim through the stomach’s protective mucus, which normally acts as a thick gel barrier. The ammonia thins the mucus from a gel into a liquid, allowing the bacteria to reach the stomach lining and attach to the cells beneath. Over time, this triggers chronic, low-grade inflammation, but that inflammation doesn’t always produce symptoms you can feel.
The Core Symptoms
When H. pylori does cause trouble, it usually takes the form of gastritis (inflammation of the stomach lining) or peptic ulcers (open sores in the stomach or upper small intestine). The symptoms overlap significantly, and you can’t reliably tell the two apart based on how you feel. Common signs include:
- Burning or gnawing upper abdominal pain, often between meals or during the night when the stomach is empty
- Bloating and excessive burping
- Nausea, sometimes with vomiting
- Loss of appetite
- Feeling full quickly after eating only a small amount
- Unexplained weight loss
The abdominal pain is the hallmark symptom. It tends to come and go over weeks or months rather than staying constant. Many people describe it as a dull ache that worsens on an empty stomach and temporarily improves after eating or taking an antacid. This pattern reflects what’s happening beneath the surface: stomach acid irritating inflamed or damaged tissue, with food briefly buffering that contact.
When Gastritis Becomes an Ulcer
Simple gastritis from H. pylori can simmer for years with mild, intermittent discomfort that’s easy to dismiss as indigestion. Ulcers represent a step further: the bacteria’s damage to the mucus barrier has allowed acid to erode into the stomach wall itself. Pain from an ulcer tends to be sharper and more localized, and it may wake you up at night. You might also notice that the pain follows a more predictable pattern tied to meals.
About 10% of people with H. pylori eventually develop a peptic ulcer. The shift from gastritis to ulcer doesn’t always announce itself dramatically. Sometimes the first clear sign is a complication like bleeding, which shows up as dark, tarry, or black stools, or vomit that looks like coffee grounds. These are signals that the ulcer has eroded into a blood vessel and needs immediate medical attention.
Warning Signs That Need Urgent Care
Certain symptoms suggest a serious complication, most often a bleeding ulcer. You should seek care right away if you experience:
- Black or tarry stools, which indicate bleeding in the upper digestive tract
- Vomiting blood or material that resembles dark coffee grounds
- Sharp, sudden stomach pain that doesn’t improve
- Trouble swallowing
- Unusual dizziness, fatigue, or fainting, which can signal significant blood loss
A perforated ulcer, where the sore eats entirely through the stomach wall, causes sudden, severe abdominal pain and is a medical emergency.
The Long-Term Cancer Risk
H. pylori is the strongest known risk factor for stomach cancer. Decades of chronic inflammation can, in a small percentage of carriers, lead to changes in the stomach lining that eventually become cancerous. The World Health Organization classifies the bacterium as a Group 1 carcinogen.
The difficult reality is that stomach cancer rarely produces early symptoms. By the time signs appear, the disease is often advanced. The symptoms that do emerge, such as persistent abdominal discomfort, loss of appetite, feeling full after small meals, nausea, and unintended weight loss, look nearly identical to those of a simple H. pylori infection. This overlap is one reason why testing and treating the infection matters even when symptoms seem manageable.
How H. Pylori Is Diagnosed
If your symptoms point toward H. pylori, several tests can confirm it. The most accurate noninvasive option is the urea breath test, which has a sensitivity of about 96% and specificity around 88%. You swallow a small amount of a labeled compound, and if H. pylori is present, its enzyme breaks it down in a way that’s detectable in your breath within minutes.
A stool antigen test is another noninvasive option. It’s highly specific (about 95%), meaning a positive result is very reliable, but its sensitivity is lower (around 73%), so it can miss some infections. Blood antibody tests detect past exposure but can’t distinguish between a current and a previously cleared infection, making them less useful for guiding treatment decisions.
Endoscopy, where a thin camera is passed into the stomach, remains the gold standard. It allows direct visualization of any inflammation or ulcers and enables a tissue biopsy for definitive diagnosis. It’s typically reserved for people with alarm symptoms or those who haven’t responded to initial treatment.
What Treatment Looks Like
H. pylori treatment involves a combination of antibiotics and acid-suppressing medication, taken together for 10 to 14 days. The goal is to kill the bacteria and let the stomach lining heal. Most people notice symptom improvement within the first week of treatment.
About 25% of treatment courses fail, primarily because of antibiotic-resistant strains. Resistance has been climbing globally, which means some people need a second round with a different antibiotic combination. After completing treatment, your doctor will typically retest (usually with a breath or stool test) to confirm the infection is gone. If the first course doesn’t work, a different regimen almost always does.
Once H. pylori is successfully eradicated, ulcers heal and the risk of recurrence drops substantially. The chronic inflammation that drives long-term complications, including the elevated cancer risk, also begins to reverse.