In general, pure essential oils can be subdivided into two distinct groups of chemical constituents; the hydrocarbons which are made up almost exclusively of terpenes (monoterpenes, sesquiterpenes, and diterpenes), and the oxygenated compounds which are mainly esters, aldehydes, ketones, alcohols, phenols, and oxides.
Terpenes - inhibit the accumulation of toxins and help discharge existing toxins from the liver and kidneys.
• Sesquiterpenes are antiseptic and anti-inflammatory. They work as a liver and gland stimulant and contain caryophyllene and valencene. Research from the universities of Berlin and Vienna show increased oxygenation around the pineal and pituitary glands. Further research has shown that sesquiterpenes have the ability to surpass the blood-brain barrier and enter the brain tissue. other sesquiterpenes, like chamazulene and farnesol, are very high in anti-inflammatory and anti-bacterial activity. Chamazulene may be found in chamomile, tansy, and yarrow.
• Farnesene is anti-viral in action.
• Limonene has strong anti-viral properties and has been found in 90% of the citrus oils.
• Pinene has strong antiseptic properties and may be found in high proportions in the conifer oils such as pine, fir, spruce, and juniper.
• Other terpenes include camphene, cadinene, cedrene, dipentene, phellandrene, terpinene, sabinene, and myrcene.
Esters - are the compounds resulting from the reaction of an alcohol with an acid (known as esterification). Esters are very common and are found in a large number of essential oils. They are anti-fungal, calming and relaxing.
• Linalyl acetate may be found in bergamot, Clary sage, and lavender
• Geraniol acetate may be found in sweet marjoram.
• Other esters include bornyl acetate, eugenol acetate, and lavendulyl acetate.
Aldehydes - are highly reactive and characterized by the group C-H-O (Carbon, Hydrogen, Oxygen). In general, they are anti-infectious with a sedative effect on the central nervous system. They can be quite irritating when applied topically (citral being one example), but may have a profound calming effect when inhaled.
• Citral is very common with a distinctive antiseptic action. It also has an anti-viral application as with melissa oil when applied topically on herpes simplex.
• Citronellal is also very common and has the same lemony scent as citral. Along with citral and neral, citronellas may be found in the oils of melissa, lemongrass, lemon, mandarin, lemon-scented eucalyptus, and citronella.
• Elements of aldehydes have also been found in lavender and myrrh. Other aldehydes include benzaldehyde, cinnamic aldehyde, cuminic aldehyde, and perillaldehyde.
Ketones - are sometimes mucolytic and neuro-toxic when isolated from other constituents. However, all recorded toxic effects come from laboratory testing on guinea pigs and rats. No documented cases exist where oils with a high concentration of ketones (such as mugwort, tansy, sage, and wormwood) have ever caused a toxic effect on a human being. Also, large amounts of these oils would have to be consumed for them to result in a toxic neurological effect. Ketones stimulate cell regeneration, promote the formation of tissue, and liquefy mucous. They are helpful with such conditions as dry asthma, colds, flu and dry cough and are largely found in oils used for the upper respiratory system, such as hyssop, Clary sage, and sage.
• Thujone is one of the most toxic members of the ketone family. It can be an irritant and upsetting to the central nervous system and may be neuro-toxic when taken internally as in the banned drink Absinthe. Although it may be inhaled to relieve respiratory distress and my stimulate the immune system, it should only be administered by an educated and professional aromatherapist.
• Jasmone (found in jasmine) and fenchone (found in fennel) are both non-toxic.
• Other ketones include camphor, carvone, menthone, methyl nonyl ketone, and pinacamphone.
Alcohols - are commonly recognized for their antiseptic and anti-viral activities. They create an uplifting quality and are regarded as non-toxic.
• Terpene Alcohols stimulate the immune system, work as a diuretic and a general tonic, and are anti-bacterial as well.
◦ Linalol can help relieve discomfort. It may be found in rosewood and lavender.
◦ Citronellol may be found in rose, lemon, eucalyptus, geranium, and others.
◦ Geraniol may be found in geranium as well as palmarosa.
◦ Farnesol may be found in chamommile. It is also good for the mucous.
◦ Other terpene alcohols include borneol, menthol, nerol, terpineol, (which Dr. Gattefosse considered to be a decongestant), vetiverol, benzyl alcohol, and cedrol.
• Sesquiterpene Alcohols are anti-inflammatory, anti-bacterial, anti-mycotic, and ulcer-protective (preventative).
◦ Bisabolol is one of the the strongest sesquiterpene alcohols. It may be found in chamomile oils where it also functions well as a fixative.
Phenols - are responsible for the fragrance of an oil. They are antiseptic, anti-bacterial, and strongly stimulating but can also be quite caustic to the skin. They contain high levels of oxygenating molecules and have anioxidant properties.
• Eugenol may be found in clove and cinnamon oil.
• Thymol is found in thyme and may not be as caustic as other phenols.
• Carvacrol may be found in oregano and savory. Researchers believe it may possibly contain some anti-cancerous properties.
• Others in the phenol family include methyl eugenol, methyl chavicol anethole, safrole, myristicin, and apiol.
Oxides - According to The American Heritage™ Dictionary of the English Language, an oxide is "a binary compound of an element or a radical with oxygen".
• Cineol (or eucalyptol) is by far the most important member of the family and virtually exists in a class of its own. It is anesthetic, antiseptic, and works as an expectorant. Cineol is well known as the principal constituent of eucalyptus oil. It may also be found in rosemary, cinnamon, melissa, basil, and ravensara.
• Other oxides include linalol oxide, ascaridol, bisabolol oxide, and bisabolone oxide.
Note: All pure essential oils have some anti-bacterial properties. They increase the production of white blood cells, which help fight infectious illnesses. It is through these properties that aromatic herbs have been esteemed so highly throughout the ages and so widely used during the onsets of malaria, typhoid, and of course, the epidemic plagues during the 16th century. Research has found that people who consistently use pure essential oils have a higher level of resistance to illnesses, colds, flues, and diseases than the average person. Further indications show that such individuals, after contracting a cold, flu, or other illness, will recover 60-70 percent faster than those who do not use essential oils.