— this page is the wiki’s own appraisal concept, induced across two 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).
Two held instances show the split
- Aspartame — Group 2B on limited evidence. 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.
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.