Acetaldehyde (systematically ethanol) is an organic chemical compound with the formula CH3CHO or MeCHO. 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. Pathways of exposure include air, water, land or groundwater that can expose the human subject directly if they inhale, drink, or smoke.