When you think about what causes cancer, your mind probably jumps to smoking, genetics, or unhealthy diets, not cancer causing bacteria. But scientists now know that some bacteria, quietly living inside you for years, can actually set the stage for certain types of cancer.
The most striking example? Helicobacter pylori (H. pylori) is a spiral-shaped bacterium that hides in your stomach and is responsible for most cases of stomach cancer around the world.
Let’s unpack what this means for you and how understanding the link between bacteria and cancer could help you protect your health.
H. pylori: The Bacterium You Don’t Know You Have
H. pylori infects roughly half of all people globally, often starting in childhood. Most never feel a thing—there are rarely symptoms. Yet, for a small percentage, this bacterium can quietly inflame the stomach lining for years. Over time, that chronic inflammation may lead to ulcers, pre-cancerous changes, and eventually stomach cancer.
Key facts:
- H. pylori is recognised by the World Health Organisation as a definite cause (type I carcinogen) of stomach cancer.
- Up to 90% of non-cardia gastric cancer cases worldwide are linked to H. pylori infection.
- A 2025 Nature Medicine study projects 15.6 million stomach cancer cases among those born between 2008 and 2017, with 76% directly attributed to H. pylori.
How Does a Bacterium Cause Cancer?
It starts with chronic irritation. H. pylori tunnels into the stomach lining, causing long-lasting inflammation (gastritis). Some strains produce a toxin (CagA) that interferes with normal cell repair, increasing the chance of cancerous changes. This process can take decades, which is why stomach cancer often develops later in life.
Other risk factors that make the problem worse
While H. pylori infection is a major contributor to stomach cancer, several other factors can significantly increase your risk or make existing problems worse.
- High-Salt Foods: Too much salt damages your stomach lining over time. This includes pickled foods, cured fish, and processed snacks that create chronic irritation, leading to cellular changes.
- Processed Meats: Bacon, sausages, and deli meats contain nitrates that form cancer-causing compounds in your acidic stomach environment.
- Smoking: Tobacco chemicals enter your bloodstream and directly damage stomach cells, doubling your cancer risk compared to non-smokers.
- Family History: Having close relatives with stomach cancer increases your risk due to shared genes or common lifestyle habits.
- High-Risk Regions: People from East Asia, Latin America, and Eastern Europe face higher rates due to increased H. pylori infections, traditional high-salt diets, and genetic predispositions.
The good news: many of these factors are controllable through diet changes, quitting smoking, and regular medical checkups.
Can Eradicating H. pylori Lower Your Cancer Risk?
Yes. Large studies show that treating H. pylori with a course of antibiotics, especially before pre-cancerous changes occur, can dramatically lower your risk of stomach cancer. Some countries are even piloting screening-and-eradication programs to prevent thousands of future cases.
What About Other Cancer-Linked Bacteria?
While H. pylori is the best-proven example, research continues into other bacteria that may contribute to cancers of the colon, mouth, and beyond. For now, H. pylori remains the only bacterium officially classified as a definite cancer cause by major health agencies.
Key Takeaways
Understanding that cancer causing bacteria like H. pylori exist might feel alarming at first, but it’s also empowering. While most people who carry H. pylori will never develop stomach cancer, being aware of your risk and taking proactive steps—such as early testing, timely antibiotic treatment, and adopting gut-friendly lifestyle habits—can dramatically lower your chances.
By staying informed, discussing prevention with your healthcare provider, and focusing on habits that support gut health, you take control of your long-term well-being. Early action offers the best chance to prevent problems before they start, and it’s never too late to make positive changes for your future health.
