Known for its irritant effects, formaldehyde is a substance found mainly in indoor environments where it has multiple sources: construction products, furnishings, detergents, etc. It is also emitted naturally during combustion phenomena (fires, cigarette smoking) and anthropogenic activities (cooking food, using a wood burning stove). Formaldehyde has been classified as "carcinogenic to humans" (Group 1) by the International Agency for Research on Cancer (IARC) since 2004. Following this classification, ANSES conducted a series of expert assessments concerning the general and occupational populations. In 2011, it also submitted a proposal to the European Chemicals Agency (ECHA), which led to formaldehyde’s European classification being revised to that of Category 1B carcinogen (presumed to have carcinogenic potential for humans) and Category 2 mutagen.