— this page is the wiki’s own appraisal concept, induced across the held IARC instances; the verbatim classifications and their evidence live on those instance pages, not re-extracted here.
A carcinogen classification answers whether an exposure can cause cancer at some dose, never how
much it raises your risk at the dose you meet. These are two different objects that one word — “carcinogen”
— hides, and the confusion between them drives most public cancer-scare reactions. type-B (one label,
two distinct quantities). IARC does hazard identification: is the hazard excludable, given the human,
animal, and mechanistic evidence? It does not do risk assessment: what absolute risk this exposure adds
to a given person at a realistic dose. A Group-1, 2A, or 2B label grades the strength of evidence that a
hazard exists, not the size of the risk — so the label alone licenses no avoidance decision.
The two objects, kept apart
- Hazard identification (what IARC does). Can this exposure cause cancer at any dose? The group (1 / 2A / 2B) reports how firmly that yes-or-no is established — sufficient, limited, or inadequate evidence in humans, combined with animal and mechanistic data. It is a statement about evidence of existence, close in spirit to a GRADE certainty rating -> Certainty of Evidence vs Strength of Recommendation.
- Risk magnitude (what the label omits). How much does this exposure raise your absolute risk, at your exposure, over your baseline? That is a relative effect applied to a baseline risk — the quantity a decision actually needs -> Baseline Risk and the Relative-Absolute Split. A large relative effect on a tiny baseline is a tiny absolute risk; a firm hazard classification says nothing about where on that scale an exposure sits.
Two exposures can share a hazard group and differ in risk magnitude by orders of magnitude. This is why the public alarm that a food “shares a category with tobacco” is a category error: the shared category is a statement about evidence that a hazard exists, and it is silent on the risk each one actually carries. The fabric routes the processed-meat decision itself through absolute risk, not through its hazard label -> Red and Processed Meat and Cancer (the wiki does not hold IARC’s processed-meat monograph, so the Group-1 label is noted as the public framing, not asserted as a fabric finding).
Held instances show the split — a firm label sits atop a large or a negligible risk
- Aspartame — Group 2B, risk near zero. IARC classified aspartame “possibly carcinogenic” on limited human evidence — explicitly a hazard identification, not a dose or risk statement, and JECFA’s companion intake evaluation left the acceptable daily intake unchanged. The label reads as alarming; the risk statement attached to a realistic intake did not move -> Non-Sugar Sweeteners.
- Night-shift work — Group 2A, later contested on risk. IARC’s probable-carcinogen classification rested on limited human plus sufficient animal evidence (a hazard judgement); a large prospective analysis then found the exposure has little or no effect on breast-cancer incidence. The clearest demonstration of the split: an exposure can be firmly classified as a probable hazard and still carry a risk magnitude near zero -> Night Shift Work and Breast Cancer.
- Dietary acrylamide — Group 2A, risk near zero at dietary dose. A probable carcinogen on genotoxic and animal evidence, yet human dietary exposure sits four-to-five orders of magnitude below the rodent-carcinogenic dose; the page reads the hazard identification and the dietary-dose risk as different questions that do not conflict — the same split, reached in this concept’s own terms -> Dietary Acrylamide and Cancer Risk.
- Alcohol — Group 1, risk large. The three instances above are all evidence-firm-enough yet magnitude-negligible; alcohol is the held case where a firm label and a large risk coincide. It is an established (Group 1) carcinogen whose risk magnitude is real and dose-dependent, with no safe threshold for the aerodigestive and breast sites, and it ranks among the leading attributable causes of cancer -> Alcohol and Cancer Risk. Set beside night-shift work (Group 2A, risk near zero), it makes the point concrete in the decision-relevant direction: the classification grades the evidence that a hazard exists, not its size, so the label alone cannot tell you the magnitude — you must look up the absolute risk. A firmly established hazard (alcohol) can carry a large risk; a probable one (night-shift, acrylamide) can carry near zero.
The honest limit on what these four instances show. They happen to line up group-with-magnitude — the one large risk is the Group-1 case, the three negligible ones are 2A/2B — so they do not demonstrate that group and magnitude are independent (there is no held Group-1 with a small risk, nor a 2A/2B with a large one). What they show is narrower and still decision-relevant: a firm label is compatible with either a large or a negligible risk, so the label is not a substitute for the risk number. The stronger same-group/different-magnitude illustration — alcohol against the small absolute effect of Group-1 processed meat — needs a held Group-1 pair the wiki does not yet carry -> Red and Processed Meat and Cancer.
Decision relevance
- A hazard label is not an avoidance decision. Do not decide to avoid an exposure because it carries a carcinogen classification. The classification tells you the hazard is real enough to take seriously as a question; it does not tell you the risk is large enough to act on. Ask for the absolute risk — relative effect on your baseline — before changing anything.
- Match the response to the risk magnitude, not the category. The same Group-1/2A/2B language spans exposures whose absolute risks differ enormously; a proportionate response tracks the risk number, which the label does not carry.
- The certainty of the hazard and the size of the risk move independently. A firmly established hazard (high evidential certainty) can add a negligible risk, and a suspected hazard on limited evidence can — if real — add a large one. Keep the two questions separate, the way GRADE keeps certainty apart from the strength of a recommendation -> Certainty of Evidence vs Strength of Recommendation.