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Stable for nowRetrospective

How we learned that bacteria — not stress — cause most stomach ulcers

For most of the 20th century, peptic ulcers were blamed on stress and excess stomach acid. Beginning in 1982, two researchers in Perth argued the real culprit was a bacterium, Helicobacter pylori. The idea was dismissed for years — then became medical consensus, and a Nobel Prize.

Where the claims stand

3 corroborated1 supported1 contradicted

We’ll only notify you when something material changes.

Status

Stable for now

The core questions here were settled decades ago by independent replication, an NIH consensus panel, and a Nobel Prize. We show it as a finished arc.

Confidence — today

as of May 19, 2026

We are highly confident that most peptic ulcers are caused by H. pylori infection (with NSAIDs the other major cause), because the bacterial hypothesis was independently replicated, endorsed by a 1994 NIH consensus panel, and recognized with the 2005 Nobel Prize in Physiology or Medicine. This reflects decades of accumulated evidence, not a single study.

This is our best read given published evidence today — not a claim of absolute truth.

Open questions

  • Why do most people infected with H. pylori never develop an ulcer?

    Infection is common worldwide, but only a minority develop ulcers or gastric cancer — host genetics, bacterial strain, and environment all appear to matter.

  • How should rising antibiotic resistance change first-line treatment?

    Standard triple therapy is becoming less reliable as resistance grows, which affects how today's ulcers are cured.

What would change our mind

  • Large, well-controlled studies showing antibiotic eradication does not reduce ulcer recurrence.
  • Replicated evidence that the original biopsies and cultures were systematically contaminated.

Claims & evidence

Each claim is tracked separately — not a single verdict.

  • Most peptic ulcers are caused by H. pylori infection, not primarily by stress or spicy food.

    Corroborated
    Evidence basisPeer-reviewed · independently corroborated

  • H. pylori survives in the acidic stomach, largely by using the enzyme urease to neutralize acid locally.

    Corroborated
    Evidence basisOfficial statement · single source

  • Antibiotic eradication of H. pylori cures most peptic ulcers and sharply reduces recurrence.

    Corroborated
    Evidence basisOfficial statement · single source

  • Peptic ulcers are primarily caused by psychological stress and excess gastric acid.

    Contradicted
    Evidence basisOfficial statement · single source

  • Chronic H. pylori infection is a major risk factor for gastric cancer.

    Supported
    Evidence basisOfficial statement · single source

How we got here

5 updates · append-only
  1. Official confirmation

    The 2005 Nobel Prize recognizes the discovery — the arc closes

    Warren and Marshall are awarded the Nobel Prize in Physiology or Medicine for the discovery of H. pylori and its role in gastritis and peptic ulcer disease. A claim once dismissed as implausible is now textbook medicine.

    What changed

    • Status: Partially corroborated Stable for now
    • Claim: stress/acid as primary cause: Weakened Contradicted
  2. Official confirmation

    An NIH consensus panel endorses the bacterial cause and antibiotic treatment

    After a decade of replication and antibiotic trials, a U.S. National Institutes of Health consensus panel concludes that H. pylori has a major role in peptic ulcer disease and recommends antibiotics in addition to acid suppression.

    What changed

    • Claim: cause of most peptic ulcers: Stress and excess acid H. pylori infection (consensus)
    • Status: Contested Partially corroborated
  3. New evidence

    WHO's cancer agency classifies H. pylori as a Group 1 carcinogen

    The International Agency for Research on Cancer concludes there is sufficient evidence that chronic H. pylori infection causes gastric cancer in humans, raising the stakes of the once-dismissed hypothesis.

    What changed

    • Claim: H. pylori and gastric cancer: Suspected association Sufficient evidence of carcinogenicity (Group 1)
  4. New evidence

    A self-experiment puts the hypothesis to a hard test

    Frustrated by skepticism, Barry Marshall drinks a culture of the bacterium and develops acute gastritis, providing dramatic (if anecdotal) support that the organism can colonize a healthy stomach and cause inflammation.

    What changed

    • Claim: H. pylori can colonize the stomach: Unverified Supported by direct (anecdotal) human evidence
  5. New evidence

    A spiral bacterium is cultured from the stomach — and blamed for ulcers

    Robin Warren and Barry Marshall, working in Perth, Australia, repeatedly find a spiral bacterium in stomach biopsies and propose it causes gastritis and peptic ulcers. The claim runs against the prevailing belief that the stomach is too acidic for bacteria and that ulcers come from stress and acid.

    What changed

    • Leading explanation for ulcers: Stress and excess gastric acid (prevailing view) New hypothesis on record: bacterial infection (H. pylori)

Suggest a source

Point us to a primary source or a publisher correction. Every suggestion is reviewed by a human before anything changes — this is not voting on what’s true.

Confidence last reviewed May 19, 2026. Updates are append-only; nothing here is edited silently.