Who defines carcinogens and what determines the risk level of a carcinogen?

Who defines carcinogens and what determines the risk level of a carcinogen?

There are a number of agencies and organizations whose function is to identify and classify the carcinogenic potential of various substances and factors.  One of these is the International Agency for Research on Cancer (IARC), established by the World Health Organization (WHO) in 1965, as a scientific branch for research on cancer.  The aims of this agency (today comprising 22 countries) are to promote research towards understanding the causes of cancer, and to advance the means to prevent and reduce cancer morbidity.

IARC publishes comprehensive reviews (monographs) summarizing the research on the effects of environmental factors that may increase the risk of developing cancer in humans.  This information is used by health authorities in countries around the world, to assist them in policy-making regarding the prevention of exposure to carcinogenic agents.

The reviews are conducted by multidisciplinary working groups of expert scientists from different countries.  The groups review the accumulated up-to-date published scientific information on a specific agent, and classify it under one of 5 categories according to its carcinogenic potential in humans:

Group 1: Carcinogenic to humans

Group 2A: Probably carcinogenic to humans

Group 2B: Possibly carcinogenic to humans

Group 3: Not classifiable as to its carcinogenicity to humans

Group 4: Probably not carcinogenic to humans