Butyric acid (from Ancient Greek: meaning "butter"), also known under the systematic name butanoic acid, is a carboxylic acid with the structural formula CH3CH2CH2-COOH. Salts and esters of butyric acid are known as butyrates or butanoates. Butyric acid is found in animal fat and plant oils, bovine milk, breast milk, butter, parmesan cheese, and as a product of anaerobic fermentation (including in the colon and as body odor). Butyric acid has a taste somewhat like butter and an unpleasant odor. Mammals with good scent detection abilities, such as dogs, can detect it at 10 parts per billion, whereas humans can only detect it in concentrations above 10 parts per million. In food manufacturing, it is used as a flavoring agent.
Butyric acid is a biologically active compound in humans. Butyric acid is one of two primary endogenous agonists of human hydroxycarboxylic acid receptor 2 (HCA2), a Gi/o-coupled G protein-coupled receptor.