3-Methylbutanoic acid, or more commonly isovaleric acid, is a natural fatty acid

Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 found in a wide variety of plants and essential oil

Essential oil

An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...

s. Isovaleric acid is clear colorless liquid that is sparingly soluble in water, but extremely soluble in most common organic solvents.

Isovaleric acid has a strong pungent cheesy or sweaty smell, but its volatile ester

Ester

Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

s have pleasing scents and are used widely in perfumery. It has been proposed that it is the anticonvulsant

Anticonvulsant

The anticonvulsants are a diverse group of pharmaceuticals used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of bipolar disorder, since many seem to act as mood stabilizers, and in the treatment of neuropathic pain. The goal of an...

 agent in valerian

Valerian (herb)

Valerian is a hardy perennial flowering plant, with heads of sweetly scented pink or white flowers which bloom in the summer months. Valerian flower extracts were used as a perfume in the sixteenth century....

. It is a major component of the cause of unpleasant foot odor. Isovaleric acid is what gives stale hops

Hops

Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...

its characteristically cheesy aroma and flavor.

Other synonyms include delphinic acid, 3-methylbutyric acid, and isopentanoic acid.