Terpenes are a group of unsaturated aliphatic cyclic hydrocarbons, which, unlike petroleum distillates, are derived from plants. Their widespread functions range from comprising building blocks of useful compounds to rubefacients and cleaning substances. The best-known substances in this group are pine oil, turpentine, and camphor oil. They are classified in chemical groups depending upon the number of isoprene units contained. For example, monoterpenes, such as cantharidin found in Spanish fly or blistering beetle, have a 10-carbon structure, as does turpentine.
All terpenes are local irritants.
Renal toxicity has been reported. Following ingestion, pine oil may be concentrated in the lungs, resulting in chemical pneumonitis without evidence of aspiration. Absorption may begin in the oral cavity. Terpenes are oxidized by cytochrome P450, conjugated principally with glucuronic acid in the liver, and are excreted by the kidney. The excretory product of turpentine has a characteristic odor of violets.