Plicatic acid is a carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

 from the resin acid

Resin acid

Resin acids usually refers to mixtures primarily. Abietic acid is the main component but several related carboxylic acids. Nearly all resin acids have the same basic skeleton: three fused ring fused with the empirical formula C19H29COOH. These materials occur in rosin but also occur in fossil...

 group. It is naturally found in thuja

Thuja

Thuja is a genus of coniferous trees in the Cupressaceae . There are five species in the genus, two native to North America and three native to eastern Asia...

 and cypress

Cupressaceae

The Cupressaceae or cypress family is a conifer family with worldwide distribution. The family includes 27 to 30 genera , which include the junipers and redwoods, with about 130-140 species in total. They are monoecious, subdioecious or dioecious trees and shrubs from 1-116 m tall...

 resin. It is the main irritant and contact allergen present in thuja wood. (Cf. pine

Pine

Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...

, where the primary irritant is abietic acid

Abietic acid

Abietic acid , an organic compound that occurs widely in trees. It is the primary component of resin acid, is the primary irritant in pine wood and resin, isolated from rosin and is the most abundant of several closely related organic acids that constitute most of rosin, the solid portion of the...

.)

The highest concentrations of plicatic acid can be found in Thuja plicata

Thuja plicata

Thuja plicata, commonly called Western or pacific red cedar, giant or western arborvitae, giant cedar, or shinglewood, is a species of Thuja, an evergreen coniferous tree in the cypress family Cupressaceae native to western North America...

(Western Redcedar), but Thuja occidentalis

Thuja occidentalis

Thuja occidentalis is an evergreen coniferous tree, in the cypress family Cupressaceae, which is widely cultivated for use as an ornamental plant known as American Arbor Vitae. The endemic occurrence of this species is a northeastern distribution in North America...

(Eastern Arborvitae) and Cryptomeria japonica

Cryptomeria

Cryptomeria is a monotypic genus of conifer in the cypress family Cupressaceae formerly belonging to the family Taxodiaceae; it includes only one species, Cryptomeria japonica . It is endemic to Japan, where it is known as Sugi...

(Sugi) contain it in significant proportions as well.

Exposure to plicatic acid or thuja wood dust can worsen asthma

Asthma

Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

 and provoke allergic reactions.