H. pylori (Helicobacter pylori) is a type of bacteria that infects the stomach lining. It’s one of the most common infections on the planet: more than half the world’s population carries it, with an estimated 4.4 billion people infected globally as of 2015. Most people with H. pylori never feel sick from it, but in some cases, the infection causes stomach ulcers, chronic inflammation, and raises the risk of stomach cancer.
How H. Pylori Survives in the Stomach
Your stomach is an extremely acidic environment, hostile to nearly all bacteria. H. pylori gets around this with a clever trick. It produces large amounts of an enzyme called urease, which breaks down urea (a normal waste product in your body) into ammonia and carbon dioxide. The ammonia neutralizes the acid immediately surrounding the bacterium, creating a small pocket of neutral pH where it can thrive.
This acid-neutralizing process also helps H. pylori move. The stomach lining is coated in a thick, gel-like layer of mucus that would normally trap bacteria. But when H. pylori raises the pH around itself, that mucus gel becomes more liquid, allowing the bacterium to swim freely through it and burrow into the stomach wall. Once embedded in the lining, the infection can persist for decades if untreated.
How It Spreads
H. pylori passes from person to person, most likely through saliva, contaminated water, or contact with vomit or stool. Infection rates vary dramatically by region. Africa has the highest prevalence at roughly 70%, while Oceania has the lowest at about 24%. At the country level, rates range from around 19% in Switzerland to nearly 88% in Nigeria. Most people acquire the infection during childhood, often through close contact within families.
Symptoms to Watch For
Most H. pylori infections don’t cause any noticeable symptoms. When they do, the most common signs include:
- A burning or aching pain in the stomach area, often worse on an empty stomach
- Frequent burping and bloating
- Nausea or upset stomach
- Loss of appetite
- Unexplained weight loss
These symptoms overlap with many other digestive conditions, which is why testing is important if they persist. Stomach pain that worsens when you haven’t eaten and improves temporarily after eating is a particularly common pattern with H. pylori-related ulcers.
How H. Pylori Is Diagnosed
There are several reliable ways to test for H. pylori, and none of them require blood draws.
Breath Test
The urea breath test is one of the most common methods. You breathe into a container, then swallow a pill or liquid containing a special form of urea. If H. pylori is present in your stomach, the bacteria break down the urea and release carbon dioxide with a detectable chemical signature. A few minutes later, you breathe into the container again. If the second sample contains more of that tagged carbon dioxide, the test is positive.
Stool Test
A stool antigen test looks for proteins produced by H. pylori in a stool sample. This is a straightforward, noninvasive option and is widely used for both initial diagnosis and confirming that treatment has worked.
Endoscopy
If other tests are inconclusive or your symptoms are more severe, a doctor may perform an endoscopy. This involves threading a thin, flexible tube with a camera down your throat and into your stomach while you’re sedated. During the procedure, small tissue samples can be taken from the stomach lining and tested directly for the bacteria. An endoscopy also allows the doctor to visually check for ulcers or other damage.
Complications of Untreated Infection
Left untreated over years, H. pylori can cause chronic inflammation of the stomach lining (gastritis), which may progress to peptic ulcers in the stomach or upper small intestine. The bacterium is also a well-established risk factor for stomach cancer. The World Health Organization classified H. pylori as a carcinogen decades ago, and it remains the strongest known risk factor for gastric cancer specifically. Not everyone with H. pylori develops cancer, but chronic, long-term infection significantly increases the odds.
How H. Pylori Is Treated
Treatment involves taking a combination of medications for 14 days. The current recommended approach for most people who haven’t been treated before is bismuth-based quadruple therapy: an acid-reducing medication taken twice daily alongside three other drugs, including two antibiotics and a bismuth compound (the active ingredient in products like Pepto-Bismol). This combination attacks the bacteria from multiple angles while reducing stomach acid to help the lining heal.
An older approach using a single antibiotic called clarithromycin was once the standard, but guidelines from the American College of Gastroenterology now recommend against it unless lab testing has confirmed the bacteria are susceptible to that drug. The reason: antibiotic resistance has become a serious problem. Globally, resistance to clarithromycin exceeds 15% in the majority of countries studied. In parts of Asia, resistance rates have climbed as high as 50%. Resistance to another commonly used antibiotic, levofloxacin, shows a similar trend, reaching over 40% in North America.
Some antibiotics still work well in most parts of the world. Resistance to tetracycline remains below 1% globally, and resistance to amoxicillin stays under 2% in most countries, though parts of Africa are a notable exception with rates above 70%. After finishing treatment, your doctor will typically retest you (usually with a breath or stool test) to confirm the infection has been cleared. If the first round doesn’t work, alternative drug combinations are available.
Who Should Get Tested
Testing makes sense if you have persistent upper stomach pain, a history of peptic ulcers, or a family history of stomach cancer. In regions where H. pylori is very common, screening may be recommended even without symptoms. If you’ve been diagnosed and treated, follow-up testing is important because reinfection and treatment failure both occur, and rising antibiotic resistance means the first attempt doesn’t always succeed.