Substances or environmental factors can trigger cancer. They can therefore be carcinogenic or cancer-causing. The technical jargon also refers to carcinogenicity. But what exactly does carcinogenic mean? In biological terms, it means that a substance or an environmental factor causes considerable and, above all, irreparable damage to our genetic material. However, some cancer-causing substances do not act directly on our genetic material, but permanently alter important metabolic processes in the cell, as the NZZ writes."Both disruptive processes lead to the affected cell multiplying uncontrollably. A cancerous growth, a tumor, forms." There are two main classifications for classifying carcinogenicity. Those of the EU and those of the IARC (International Agency for Research on Cancer).

EU classification

The EU classifies chemical substances into the following categories:

  • Category 1A: Substances known to be carcinogenic in humans.
  • Category 1B: Substances that are probably carcinogenic in humans.
  • Category 2: Substances suspected of being carcinogenic in humans.

Classification according to IARC

IARC has same gradations but different numbering and also classifies non-chemical substances into categories:

  • Group 1: carcinogenic to humans.

To date (as of August 2023), 127 substances/substance groups have been classified in Group 1, including alcoholic beverages, diesel engine exhaust, processed meat (sausage, ham), wood dust, leather dust, and tobacco smoke.

  • Group 2A: probably carcinogenic

95 substances/substance groups have been classified in group 2A so far (as of August 2023), including acrylamide, red meat (e.g. meat from beef, pork or sheep), very hot beverages (more than 65°C), open fireplaces, shift work (night work)

  • Group 2B: possibly carcinogenic

353 substances/substance groups have been classified in group 2B so far (as of August 2023), including lead, diesel fuel (shipping), mobile phone radiation.

Substances that cannot be classified are listed in a Group 3. That is (as of August 2023) 500 substances. A fourth category includes substances classified as harmless. The IARC website allows a search for substances. However, the entry must be made in English. For example, if you search for "red meat" or "hot beverages," you will get a classification of 2A. The fungicide "chlorothalonil" appears in category 2B. It is therefore "possibly carcinogenic" according to the IARC. Chlorothalonil thus poses a lower cancer risk than sausage (group 1) or hot drinks (group 2A).

It is important to note that the classification of cancer risks says nothing about the concrete danger to which a person is exposed when coming into contact with the substance. The quantity and frequency of contact are decisive in assessing the risk.


International Agency for Research on Cancer: Agents Classified by the IARC Monographs, Volumes 1–134

International Agency for Research on Cancer: List of Classifications

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