Acetaldehyde

Acetaldehyde (systematically ethanal) is an organic chemical compound with the formula CH₃CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part of their normal metabolism. It is also produced by oxidation of ethanol and is popularly believed to be a cause of hangovers from alcohol consumption through drinking spirits. Pathways of exposure include air, water, land or groundwater as well as drink and smoke.

http://en.wikipedia.org/wiki/Acetaldehyde