Abietic acid (also known as abietinic acid or sylvic acid), a resin acid, is the primary irritant in pine wood and resin, isolat

Abietic acid (also known as abietinic acid or sylvic acid), a resin acid, is the primary irritant in pine wood and resin, isolated from rosin (via isomerization) and is the most abundant of several closely-related organic acids that constitute most of rosin, the solid portion of the oleoresin of coniferous trees. Its ester is called an abietate.

Abietic acid is a weak contact allergen; however, compounds resulting of its oxidation by air elicit stronger response. It is soluble in alcohols, acetone, and ethers.

Commercial abietic acid is usually a glassy or partly crystalline yellowish solid that melts at temperatures as low as 85°C (185°F). It belongs to the diterpene group of organic compounds (compounds derived from four isoprene units). It is used in lacquers, varnishes, and soaps, and for the analysis of resins and the preparation of metal resinates. It is listed in the Toxic Substances Control Act inventory.

Rosin has been used for centuries for caulking ships. It is also rubbed on the bows of musical instruments to make them less slippery. In modern times methods have been developed for improving the properties of the rosin acids, which are otherwise soft, tacky, and low-melting and subject to rapid deterioration by oxidation in air. Stability is greatly increased by heat treatment.

Rosin acids are converted into ester gum by reaction with controlled amounts of glycerol or other polyhydric alcohols. Ester gum has drying properties and is used in paints, varnishes, and lacquers.