How a bug survives stomach acid. H. pylori carries an enzyme that neutralises the acid around itself long enough to burrow under the mucus and latch onto the stomach wall for life ¹. Strains carrying the protein CagA roughly double the cancer risk of those without it ¹.

This is settled, not suggestive. H. pylori has been a Group 1 carcinogen since 1994, alongside tobacco and asbestos ², and causes about 89% of non-cardia stomach cancers worldwide ³. Eradication cuts stomach cancer incidence by 36% and its mortality by 22% ⁴; with a parent or sibling who had it, clearing the bug cut your own risk by 55% ⁵.

The ulcer effect is faster and larger. Peptic ulcers used to return in 60 to 80% of people within a year; after eradication that drops below 10% ⁶.

Who should actually check. Not everyone. The case is strong if a parent or sibling had stomach cancer; if you have or ever had a stomach or duodenal ulcer; if you have upper-stomach pain under 60; if you have unexplained iron or B12 deficiency ⁷; or if you grew up in East Asia, the Andes, Eastern Europe, or sub-Saharan Africa. Otherwise the case is weaker, though testing stays cheap.

Test for active infection, then treat to completion.

Bismuth quadruple is first-line because it works even against clarithromycin-resistant strains, now common worldwide ⁸.

Clear it once and it's done. If you had ulcer pain, the inflammation settles within the first month, and a year out ulcers return in under one in ten ⁶. If the bug had been draining your iron, levels climb back once you replace it ⁹. If you had no symptoms, the win is invisible but real: over the following decades your stomach stops accumulating the damage that leads to cancer ⁴. And it stays gone; where water is safe, reinfection is rare ⁷.