The short answer
Liver flukes are parasites caught from raw or undercooked freshwater fish. Long-term infection is linked to bile-duct cancer, mainly in parts of Asia. Cooking fish thoroughly prevents infection.
Two liver flukes, Opisthorchis viverrini and Clonorchis sinensis, are classified as carcinogens (WHO).
People are mainly exposed by eating raw or undercooked freshwater fish in affected regions.
It is most strongly linked to bile-duct cancer (cholangiocarcinoma).
A carcinogen classification describes hazard — whether something can cause cancer — not your personal risk at a given exposure.
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The simple version
Liver flukes are small parasitic worms. People can pick them up by eating raw or undercooked freshwater fish. Over many years, infection can inflame the bile ducts and lead to a cancer there. WHO says these infections are most common in East Asia and South America.
What liver flukes are
Two liver flukes are classified as carcinogenic to humans. They are Opisthorchis viverrini and Clonorchis sinensis. People become infected by eating raw or undercooked freshwater fish that carries the parasite. The fluke then lives in the bile ducts.
How people are exposed
Infection almost always comes from food:
- Eating raw or undercooked freshwater fish, crustaceans or vegetables that carry the parasite larvae (WHO).
The cancer connection
Long-term liver-fluke infection is linked to cholangiocarcinoma. That is a cancer of the bile ducts.
WHO says both parasites are classified as carcinogens by international health authorities.
Hazard is not the same as risk
Calling liver flukes a carcinogen says they can cause cancer under some conditions. It does not predict your personal risk. Ask your care team about yours.
How to lower your exposure
- Cook freshwater fish thoroughly before eating it.
- Avoid raw freshwater fish in areas where these infections occur.
- Known infections can be treated with medicine. Ask your care team if you think you may have one.
To see where liver flukes sit among all the things that affect cancer risk, read our overview of cancer prevention and what raises cancer risk.
The bottom line
Two liver flukes are classified as carcinogens. The key step is simple. Freshwater fish should be fully cooked. The World Health Organization notes that infection comes from eating raw fish, crustaceans or vegetables that harbour the larvae.
Common questions
Does liver flukes cause cancer?
Chronic infection with two liver flukes, Opisthorchis viverrini and Clonorchis sinensis, can progress to bile-duct cancer, according to WHO. How much any one person's risk rises depends on how much they are exposed to and for how long.
How are people exposed to liver flukes?
People become infected by eating raw fish, crustaceans or vegetables that harbour the parasite larvae (WHO).
Which cancers are linked to liver flukes?
It is most strongly linked to bile-duct cancer (cholangiocarcinoma).
How can I reduce my exposure to liver flukes?
The main step is cooking freshwater fish thoroughly. Medicines can treat infection; ask your care team.
Does a carcinogen label mean I will get cancer?
No. A classification is about hazard — whether liver flukes can cause cancer under some conditions — not a prediction that any one exposed person will develop cancer. Your actual risk depends on the amount and length of exposure and other factors.
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Last updated: 2026-10-16Next planned review: 2028-07-05
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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