Butyric acid (from Greek βούτυρος = butter), also known under the systematic name butanoic acid, is a carboxylic acid with the structural formula CH3CH2CH2-COOH. (C4H8O2)
It is found in rancid butter, parmesan cheese, vomit, and body odor and has an unpleasant smell and acrid taste, with a sweetish aftertaste (similar to ether).
Butyric acid can be detected by mammals with good scent detection abilities such as dogs at 10 ppb, whereas humans can detect it in concentrations above 10 ppm.