Essential oils, also known as volatile oils, refer to the general term for a class of volatile oily components found in plants that have an aromatic odor, can be distilled with water vapor or extractants, and are immiscible with water. Volatile oils are a type of mixture with complex components, and the components extracted from different plants vary. At present, the main methods for extracting volatile oils are steam distillation and pressing. The vast majority of volatile oils are lighter than water, and only a few volatile oils are heavier than water, such as clove oil, cinnamon oil, etc., generally between 0.850 and 1.180. Therefore, most volatile oils belong to light oils, while there are also a few heavy oils.
Volatile oils are poorly soluble in water but can be completely dissolved in absolute ethanol, diethyl ether, chloroform, and fatty oils. They can dissolve in varying amounts in aqueous ethanol solutions of different concentrations – the lower the ethanol concentration, the less the volatile oil dissolves. Volatile oils can slightly dissolve in water, imparting their unique aroma to the aqueous solution. In medicine, this property is often utilized to prepare aromatic waters and injections, such as mint water, Houttuynia cordata injection, Bupleurum injection, etc.
Most Chinese herbal medicines containing volatile oils or the extracted volatile oils generally have effects such as diaphoresis, regulating qi, relieving pain, antibacterial activity, and flavor correction. Volatile oils from traditional Chinese medicines are a class of active components composed of multiple constituents. In addition to containing aliphatic and aromatic hydrocarbons and oxides, they mostly contain terpenoids, which exhibit good antibacterial effects.
