Approximately 3,000 essential oils exist throughout the world, most of which are used in the local areas from which they derive. 300 essential oils are in general use worldwide. It is helpful to know the origin of the essential oils since the origin determines their properties and characteristics. For example, geranium oils can come from Egypt, China or Madagascar - each of which has its specific characteristics.

Interestingly, the same plant can produce an oil with different properties depending on the nature of the environment in which it was grown (i.e. damp or dry soil, high or low altitude, hot or cold climate). Some oils have hundreds of biological compounds and others have few; some components are present in large amounts and others are present in very small amounts. For example, within the essential oil yuzu, there are 124 identified compounds, including 44 alcohols, 26 hydrocarbons, 12 esters, 9 ketones, 14 aldehydes, 3 phenols, and 16 miscellaneous others. The healing quality of essential oils is usually attributed to the naturally occurring chemical within them. Alcohol, for example, is said to be antibacterial and coumarins are known to be sedating.

There are a variety of methods of establishing the compounds in essential oils. The best method of analyzing the makeup of essential oils is to use several procedures together to determine the chemical components. Capillary gas-liquid chromatography reveals the chemical components, and optical rotation determines the level of purity of the essential oil. Specific gravity is measured to determine that the essential oil has the correct weight. The refractive index establishes whether the material reflects the correct angle of sodium light. Together these tests determine the purity of the essential oil.