Acetaldehyde is a probable or possible carcinogen in humans.[23] [28] In 1988 the International Agency for Research on Cancer stated, "There is sufficient evidence for the carcinogenicity of acetaldehyde (the major metabolite of ethanol) in experimental animals."[29] In October 2009 the International Agency for Research on Cancer updated the classification of acetaldehyde stating that acetaldehyde included in and generated endogenously from alcoholic beverages is a Group I human carcinogen.[30] In addition, acetaldehyde is damaging to DNA[31] and causes abnormal muscle development as it binds to proteins.