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.
Choose how you want to understand this
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 something related but broader. To protect the nation's air, water, and land, it not only asks whether a chemical can cause cancer but also estimates how much exposure leads to how much risk. That extra step — risk assessment — is what allows the EPA to 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 individual chemicals, including cancer, and develop values that describe how risk rises with exposure. Those values feed into practical decisions:
- Drinking-water standards (like the limits for arsenic and certain PFAS).
- Air-toxics rules for industrial emissions.
- Cleanup goals for contaminated sites.
The EPA's cancer descriptors
Rather than IARC's numbered groups, the EPA uses descriptive phrases, 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 evidence, similar in spirit to hazard classifications, but the EPA pairs them with quantitative risk estimates.
Why the EPA and IARC can seem to disagree
The most famous example is glyphosate. IARC classified it as probably carcinogenic — 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 — a risk-based judgment about real-world use.
Both groups reviewed serious science. They reached different-sounding conclusions largely because they were answering different questions: IARC focused on hazard; the EPA focused on risk at realistic exposure levels. Recognizing this prevents the mistake of thinking 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 scientific findings into the limits that actually protect you — the standards for your tap water, the rules on industrial pollution, the goals for cleaning up contaminated sites. When you want to know not just whether something can cause cancer but how much it matters at real exposure levels, risk assessments like the EPA's are the tool designed to answer that.
Words to know
Tap any term to see what it means.
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.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Test your knowledge
0 of 4 answered
This quiz checks understanding of educational content only. It is not medical advice. Open this quiz on its own page.