The most authoritative information on the possible carcinogenic effects of formaldehyde is provided by IARC. Formaldehyde is classified by IARC as a Group 1 agent (carcinogenic to humans). The basis of this classification is described in IARC Monograph 100 (International Agency for Research on Cancer 2012), with further detail in an earlier monograph (International Agency for Research on Cancer 2006). The carcinogenicity classification of formaldehyde is based on strong evidence that it causes cancer of the naso-pharynx and (myeloid) leukaemia in humans, with strong suggestion of a link also with sino-nasal cancer. There was a request in the recent monograph to repeat some leukaemia studies due to the uncertain significance of the research results. The IARC assessment is based on sufficient evidence in humans and sufficient evidence in animals of the carcinogenicity of formaldehyde. Other organisations have classified
formaldehyde similarly to IARC.