The International Agency for Research on Cancer (IARC) is a cross-governmental agency under the World Health Organization (WHO), and IARC is responsible for researching the causes of cancer. According to IARC, a carcinogen is a substance that can increase the occurrence of malignant tumors, and under certain conditions, chemicals that induce benign tumors may also be considered chemical carcinogens. Carcinogens are classified into 3 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). For unclassified articles, one should not infer the absence of carcinogenicity or overall safety. The categorization in the list only indicates the intensity of a substance's hazard but does not confirm the likelihood of its risk, and should be used for reference only.