The short answer
The EPA evaluates chemicals for cancer risk, often through its IRIS program, and estimates how much exposure leads to how much risk. Unlike IARC's hazard labels, the EPA's approach is more risk-based, informing limits on air, water, and workplace exposures.
The EPA assesses chemicals to protect air, water, and land in the U.S.
Its IRIS program evaluates health effects, including cancer.
The EPA uses cancer descriptors like 'likely to be carcinogenic to humans.'
Its approach is more risk-based: it estimates how much exposure leads to how much risk.
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The full explanation.
A different job than IARC
The IARC groups and the NTP Report on Carcinogens answer one question: can this cause cancer? That is hazard identification.
The U.S. Environmental Protection Agency (EPA) does a related but broader job. It has to protect the nation's air, water, and land. So it asks whether a chemical can cause cancer, and it also estimates how much exposure leads to how much risk. That extra step is called risk assessment, and it is what lets the EPA set real-world limits.
IRIS: the EPA's evaluation program
Much of this work happens through the Integrated Risk Information System (IRIS). IRIS scientists review the health effects of single chemicals, cancer among them. They then work out values that show how risk climbs as exposure climbs. Those values feed into practical decisions:
- Drinking-water standards, such as the limits for arsenic and certain PFAS.
- Air-toxics rules for industrial emissions.
- Cleanup goals for contaminated sites.
The EPA's cancer descriptors
The EPA does not use IARC's numbered groups. It uses descriptive phrases instead, such as:
- Carcinogenic to humans
- Likely to be carcinogenic to humans
- Suggestive evidence of carcinogenic potential
- Inadequate information to assess carcinogenic potential
- Not likely to be carcinogenic to humans
These describe the weight of the evidence, much as hazard classifications do. But the EPA pairs them with numbers that estimate risk.
Why the EPA and IARC can seem to disagree
The most famous example is glyphosate. IARC classified it as probably carcinogenic. That is a hazard judgment about whether it can cause cancer under some conditions. The EPA concluded it is not likely to be carcinogenic to humans at expected exposures. That is a risk-based judgment about real-world use.
Both groups reviewed serious science. Their conclusions sound different mainly because they were answering different questions. IARC looked at hazard. The EPA looked at risk at realistic exposure levels. Once you see that, you stop assuming one agency must be "wrong." It is another face of the hazard-versus-risk distinction.
Why this matters to you
The EPA's risk-based work is what turns science into the limits that actually protect you. Those include the standards for your tap water, the rules on industrial pollution, and the goals for cleaning up contaminated sites. Sometimes you want to know more than whether something can cause cancer. You want to know how much it matters at the levels you really meet. Risk assessments like the EPA's are built to answer that.
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Common questions
What is IRIS?
The Integrated Risk Information System is an EPA program that evaluates the health effects of chemicals, including cancer, and develops values used to set safe exposure levels for air, water, and cleanup sites.
How is the EPA's approach different from IARC's?
IARC classifies hazard — whether something can cause cancer. The EPA also estimates risk — how much exposure leads to how much cancer — to inform limits and standards. That is why their conclusions can sound different even when both are careful.
Why did the EPA and IARC differ on glyphosate?
IARC classified glyphosate as 'probably carcinogenic' (a hazard judgment), while the EPA concluded it is 'not likely to be carcinogenic to humans' at expected exposures (a risk-based judgment). Both reviewed serious evidence and weighed it differently.
What does the EPA do with its assessments?
It uses them to set and enforce limits — like drinking-water standards, air-toxics rules, and cleanup goals — that aim to keep real-world exposures below levels of concern.
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Last updated: 2026-08-11Next planned review: 2028-07-05
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How this page was created
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. We do not employ clinicians and do not intend to — our work 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 checked line by line against the sources listed on it. That confirms the sources support what the page says. 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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