An essential oil should be accurately defined in terms of its botanic and geographic source. This is the first basic requirement for an oil to qualify as a remedy rather than a fragrance material. A practitioner must be fully confident of an oil’s actual identity in order to put it to therapeutic use.
An oil should be extracted from a plant that is botanically identified, plant- part specific and traceable to a certain geographical region. These three criteria together are what in Europe is sometimes called a ‘genuine’ oil. Although an oil’s sensory characteristics of odour, colour and consistency will often give us sufficient information about these three criteria, it should also be shown through appropriate labelling and associated documentation to fulfill these purported criteria. A certificate of authenticity provided by the producer should contain this information and include, most importantly, both the oil’s analytic physical data (specific gravity, refractive index and optical rotation) and percentages of its key chemical constituents as determined by gas chromatography.
Botanical specificity
This refers to a specific plant genus, species and possibly chemotype. If necessary, the botanical information may be documented with a certificate of authenticity or analysis.
Genus and species
Knowing an oil’s common name or even genus name often provides insufficient botanical information. An oil simply designated as ‘Lavender’ can refer to several different types of lavenders and for therapeutic use should be differentiated by type and species, among them:
• Lavandula angustifolia, Lavender, is considered the true and main type of lavender. It is especially useful for its nervous sedative, relaxant and anti- inflammatory actions. It should have a characteristic floral-sweet-herbaceous fragrance.
• Lavandula latifolia, Spike lavender, has restorative and stimulant actions used for atonic and asthenic conditions. Its aroma is similar to Lavender but with more pronounced fresh-pungent notes.
• Lavandula x fragrans, Lavendin, is a hybrid type of lavender that combines the properties of Lavender and Spike lavender. Its fragrance is similar to Lavender but with an additional mild fruity-pungent note.
Being able to differentiate both the fragrance characteristics and the clinical action of various types of lavender is clearly important in practice.
The various species of Eucalyptus oil available also present three good examples of greatly overlapping yet somewhat distinct clinical uses. This again is entirely based on specificity of genus and species.
• Eucalyptus globulus, Blue-gum eucalyptus, is generally preferred for lower respiratory conditions and, because of its good antibacterial and expectorant
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action, especially with bacterial bronchitis present. Its fragrance is strongly fresh-camphoraceous.
• Eucalyptus radiata, Narrow-leaf eucalyptus, is considered more useful for upper respiratory conditions, in addition to being thought of by some practitioners a superior antiviral. The fragrance is softer than the Blue-gum type, but with higher top notes.
• Eucalyptus camaldulensis, River red-gum eucalyptus, is similar to the Blue- gum eucalyptus but gentler in action because of its lower cineole content and softer scent, and therefore more suitable for milder infections and for treating children in general. Its fragrance is correspondingly softer and has an additional mild woody base note.
Even Jasmine absolute can be extracted from different species whose psychological effects, are quite distinct:
• Jasminum grandiflorum is the well-known Arabian jasmine, sweet and ambra in fragrance; it is euphoric, warm and emotionally nourishing and uplifting, and is often used in treating depression.
• Jasminum sambac, with its sweet, green notes is more relaxing, cooling and emotionally centring.
Other important oils where several different species exist include Abies, the firs; Picea, the spruces; Melaleuca, the melaleucas; and Salvia, the sages. For differentiations of these, see the profiles themselves.
Chemotype
In very few cases, essential oil plants will express themselves in several different chemotypes, or chemical dominance, usually written ct. or CT. Notable examples would be Ocimum (basil), Thymus (thyme) and Melaleuca (tea tree). Here the oil’s dominant type of constituent will largely colour its general therapeutic character.
• Thymus ct. linalool, Thyme linalool, has linalool as chief component, is completely non-irritant to the skin and has an excellent antifungal action. Its fragrance complex consists mainly of rich sweet-herbaceous notes.
• Thymus ct. thymol, Thyme thymol, in contrast, with its high percentage of the phenol thymol, is strongly skin-irritant and has better broad antibacterial and immunostimulant actions. Its typical fragrance is strongly herbaceous-spicy. Clearly, it is important for accurate treatment to be able to identify the right type of Thyme oil among the several types available.
Only a minority of oil plants develop chemotypes, and most possess just a small number of them. Ravintsara (Cinnamomum camphora ct. cineol), is a good example. The
genus is Cinnamomum, the species is camphora and the chemotype is cineol. In this oil, cineol is the dominant component, evidenced in its fresh-pungent scent. Ho wood oil, in contrast, is Cinnamomum camphora ct. linalool; its fragrance is strongly rosy sweet, somewhat similar to Rosewood. Most essential oils, however, only possess a single chemical dominance, thus making chemotyping unneccessary.
Plant part specificity
Every essential oil remedy is derived from a particular part of a plant, whether leaf, herb, fruit, wood, root, and so on. This also contributes to an oil’s identity. In some cases this may tell us whether the correct part was used to distill the oil in the first place. Each part of a plant yields a somewhat different scented oil with a somewhat different chemistry, as well as energetic properties, and lends itself to particular treatment applications. This principle of botanical specificity is no different than is found in the materia medicas of Western, Chinese or Ayurvedic herbal medicine.
Plants that yield several different oils, each extracted from different parts, include Clove (bud/leaf ), Cypress (twig/cone), Juniper (berry/twig), Laurel (leaf/berry), Coriander (seed/leaf ), Cinnamon (bark/leaf ), Angelica (root/seed), Pimenta (berry/ leaf ) and Lovage (root/herb). Each of these particular extractions has a typical profile of fragrance and constituents, and will emphasize a particular action and clinical usage. For example, Cinnamon bark oil with its high level of cinnamaldehyde possesses a typical fine, powdery sweet-woody aroma; used internally, it is essentially a warming stimulant for treating cold, asthenic conditions. Cinnamon leaf oil, in contrast, includes a fresh-pungent, clove-like note with its extremely high levels of eugenol; its use is mainly for treating infections and pain conditions because of its anti-infective and analgesic properties.
Geographical specificity
Each essential oil remedy is produced from a plant of a specific bioregion. It is both interesting and informative to know where and when the plant was collected and its oil extracted. Each oil should be geographically traceable. Its origin can tell us much about the type of quality and scent of an oil – as well as, in a few cases, the circumstantial chances of it being adulterated. Many of us also have actual preferences or natural affinities for oils from certain countries and regions, often based on our own cultural heritage. Currently, Lavender oil is available in significant quantities from at least six different countries, including Bulgaria, France, England, South Africa, China and Tasmania. Each region produces fine examples of this oil, but which are subtly different because of geographic and climatic variations. These variations will condition or modulate the plant’s genetic material though up- or down-regulation. In the sensory terms of fragrance, some lavenders are more green, herbaceous; others more sweet, floral or even powdery; others more pungent; others more woody, and so
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on. Likewise, they vary slightly in their proportion of chemical components (although rarely in tandem with their variations in aroma). Fragrance and chemistry both allow us to select which ones are preferred or needed for clinical use.
Vetiver oil is a good example of an oil produced in an amazing range of aromas and colors, being extracted variously in Indonesia, Madagascar, India and Haiti. Some are deep-smoky in their earthy, rooty quality, while others are more lyrical with sweet- wood and pungent notes, and others again have lush, musty-green notes. All types of Vetiver have their potential place and purpose in practice, especially in the context of psychological applications.