Carcinogens are classified based on the strength of the evidence of their carcinogenicity. The International Agency for Research on Cancer (IARC) categorizes carcinogens into groups:
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
