Essential Oils, Nature's Essence

Essential oils are concentrated plant essences. Although they are called "oils," this is something of a misnomer because most essential oils are not in fact oily, unlike vegetable oils which have been expressed from seeds or plant nuts (such as sesame, sunflower, peach kernel, and sweet almond). A few essential oils are rather viscous and others are fairly solid. Most, however, are watery, with lavender, lemon, and eucalyptus being classic examples. The color of essential oils varies, tending to be clear or yellow, although carrot is orange, spikenard is often green, and chamomile german a beautiful deep blue. Of course, essential oils are characterized most of all by their individual aromas — hence the term "aromatherapy."

Essential oils are derived from relatively few plants and, depending on the variety, only from particular parts of that plant. These include the leaves, roots, buds, twigs, rhizomes, heartwood, bark, resin, flower petals, seeds, or fruit. In some cases the whole of the plant that grows above ground is used, as in peppermint, for example. There is a huge variation in the price of different essential oils reflecting, above all, the volume of material available, but also transportation costs and growing conditions in any given year. It takes vast quantities of hand-picked, tiny jasmine petals to produce a few drops of jasmine oil while tea tree oil can be produced much more cheaply using mechanical methods to harvest the leaves of that plant. All essential oil-producing plants are different in their yield, as well. Clary sage, for example, yields 0.3 — 1% essential oil, while clove yields 10–15%. From the same volume of material, then, clove produces up to forty-five times more essential oil than clary sage.

Throughout the world, there are approximately 3,000 essential oils, most of which are used only in the local regions in which they are found. About 300 are in more general use, and are traded worldwide. It is helpful to know where a particular oil comes from because, for example, geranium oils grown in Egypt, China, or Madagascar each have their unique characteristics. Also, the same species of plant will produce an oil with different properties depending on whether it was grown in dry or damp earth, for example, or at high or low altitude, or in a hot or cold climate.

Some essential oils contain hundreds of biochemical components, while others have only a few. And some components are present in quite large proportions while many others are present only in traces. The analysis of essential oils is still at the stage where we cannot yet say exactly how many components are in any particular essential oil, because all small traces have not been identified. Indeed, they cannot be registered because the means of analysis are not yet available. Each essential oil has a unique fingerprint, and we cannot fully identify that fingerprint because parts of it are not yet "on file" — the components are simply unknown. As methods of analysis become ever more sophisticated, and as the scientific world's catalog of components enlarges, more and more ingredients will become identifiable.

The therapeutic action of essential oils is usually attributed to the naturally occurring chemicals found within them. Within the essential oil of yuzu (Citrus junos), for example, there are known to be 124 compounds, composed of 44 alcohols, 26 hydrocarbons, 12 esters, 9 ketones, 14 aldehydes, 3 phenols and 16 miscellaneous others. Other terms in the vocabulary of essential oil analysis include terpenes, coumarins, acids, ethers, and sesquiterpenes. The way these various natural chemicals interact with each other gives an essential oil its unique qualities and, some would say, explains its therapeutic properties. Alcohols can be shown to be antibacterial, for example, and coumarins sedative. (See Chapter 8.)

Various methods are used to establish the compounds in essential oils. The best form of analysis involves using several procedures in conjunction to establish the chemical components and their purity. Capillary gas liquid chromatography establishes the chemical components, while optical rotation establishes whether the essential oil has the correct optical activity — measured in terms of percentages of bend to right or-left, or "dextrorotatory" and "laevorotatory" respectively. Also, the specific gravity of the material is measured to establish that it has the correct weight, and the refractive index establishes whether the material reflects the correct angle of sodium light. Together, these tests can establish the purity of the essential oil.

Extraction

The art of extracting the essential oil from plant materials is as old as history itself. It is difficult for us now to imagine the importance of essential oils to our ancestors who relied upon them heavily for medicinal and ritual purposes, as well as for perfume. Indeed, much of the trade in ancient times involved essential oils, which were often prepared then as "unguents" (soothing or healing salves). According to archaeologist Jacquetta Hawkes, "Everybody used them" in ancient Egypt, not just the pharaohs and other dignitaries. In the lists of products important enough to be included in ancient Egyptian records, over 30 different forms of unguents are mentioned. One method of extraction employed by the Egyptians involved squeezing the plant material, such as lily flowers, in fine linen, which was held secure on a frame at one end and twisted at the other end by a group of people. They also steeped aromatic plant materials in oils and fats of various sorts which, when solid, were sometimes formed into balls or cones, and were commonly used as head or hair decorations. These decorations would slowly melt in the heat and drip down the braided hair, both conditioning the hair and perfuming the air — an ancient "time release" air freshener!

Today, by far the majority of essential oils are produced by steam distillation, which involves putting the plant material in a large closed container known as a vat, and forcing steam through it. The heat and pressure releases the tiny droplets of essential oil from the plant, which then rise with the steam out through a spiral tube known as a condenser. The condenser cools the steam, turning it to liquid. Then the oil and water are separated. Throughout the world there are many variations of steam or water distillation, such as open fire stills, but the principle remains the same — to isolate the essential oil molecules from the plant material.

The art of distillation requires accurately judging the correct combination of heat and pressure of the steam, and the length of time the plant material is subjected to it. If the steam is too hot, the essential oil can be burned. If the pressure is too high, the properties of the essential oil can be destroyed, causing the quality of the product to be reduced. Some delicate plant materials need to be exposed to long periods of very gentle steam pressure, while more robust material can be effectively distilled in shorter periods using higher temperatures and pressure.

Orange blossom, rose and lavender water are byproducts of this distillation process — they are the water from which the essential oil has been separated. During the distillation process the water becomes imbued with the aroma of the plant material. This is sold under the French name of "hydrolats" or hydrosol.

Enfleurage is a very old method of extracting essential oils, not used much today because it's very labor-intensive and time consuming. There are several versions of enfleurage which involve immersing the flower petals in a fat so that the fat pulls the essential oil from the petal and becomes saturated with it. Then the fat and essential oil are separated. Because people today do not like essential oils to come into contact with animal matter, the fats now used are usually of vegetable origin, such as cocoa butter or coconut.

One method of enfleurage involves wiping fat on both sides of glass plates, then placing flowers on them to create a tier of fat-covered glass, supported by wooden frames or "chassis." It takes quite a bit of time for the oil to be drawn from the petals — about 24 hours in the case of jasmine and two to three days for tuberose. The glass is then taken off the chassis and the petals are removed, to be replaced with fresh flowers. The process is repeated over and over again until the fat is completely saturated. To extract the essential oil from the fat, a solvent is required — hopefully a natural alcohol — which is completely evaporated, leaving behind only the essential oil. Such essential oils are called "absolutes."

Enfleurage is still used in some places and is excellent for extracting the essential oil "absolute" from delicate flower petals, Because this process is so labor-intensive, "absolutes" produced by enfleurage are usually very expensive.

A variation on enfleurage is maceration. This also involves the use of a liquid fat or oil but in this case the fat or oil is heated to a temperature of over 60 degrees Fahrenheit. The essential-oil material, which may be flowers but could also be leaves and twigs, is put in a glass container full of the fat or oil, and exposed to heat. This breaks down the plant cells containing the essential oil, which is then released into the fat or oil. The plant material is then sifted out and more fresh plant material is added. The process is repeated, sometimes for as long as a month, until the base material is completely saturated. Then, as with enfleurage, if fat is used it is subjected to solvent extraction to separate the fat or oil from the essential oil.

Expression is the method employed to extract essential oils from the oil sacs contained in the rinds of fruit such as orange, lemon, bergamot, mandarin, and tangerine. In times past this was a very labor-intensive process, involving pressing the rind into the sponges, which absorbed the essential oil, and were then squeezed out. Today it is done by machines.

Solvent extraction is often used for gums and resins, but also for other plant materials. It involves covering the plant material in a solvent, which may be a petrochemical, and then extracting the essential oil by filtering the plant material and evaporating the solvent. While this method may be perfectly acceptable to the perfume trade, good aromatherapy companies try to avoid buying essential oils and absolutes produced using petrochemical solvents.

Plant materials are also processed under low temperatures using CO2 (carbon dioxide) extraction, in which the essential oil can be produced without impairing the odor of the flowers. Essential oils produced in this way are usually expensive. However, this method works very well with flowers and plants that previously required solvent extraction, making these perfectly acceptable for use in aromatherapy treatments.

How Essential Oils Work

In aromatherapy there are two basic ways in which essential oils have an effect upon the human body: through the nose and through the skin. Aromas are volatile, meaning they disperse in the air, float, and eventually reach the nose. These aromatic molecules float up the nostrils and come into contact with nerves extending from the olfactory bulbs, and ending in two small, sticky patches at the top of the nasal cavity. When the aroma molecule hits receptors in these nerve-rich patches, it sets off a reaction that results in brain activity. This phenomenon has been observed through brain scans and other imaging techniques.

We sometimes use our mouth when we inhale. In this case the aroma molecules enter the mouth, an excellent absorption medium because it is full of delicate mucus membrane. Aromatic molecules can enter the bloodstream in this way or through the mucus membrane of the nasal cavity. The absorption potential of these two areas of the body is increasingly being explored by doctors and pharmaceutical companies, who now make preparations that are sniffed or taken sublingually — under the tongue. It is difficult to say whether a particular oil is working specifically on the olfactory nerve path system or being absorbed through mucus membrane into the bloodstream. Essential oil molecules also enter the trachea and lungs as we inhale.

Essential oils are also thought to enter the body through the skin because their molecules are extremely tiny. The surest evidence that essential oils get into the body is found in the scientific analysis of the means of excretion — perspiration, feces, urine, breath — after a certain amount of time has passed following the application of essential oils. Some oils seem to be excreted by one method while others seem to be excreted by another. For example, sandalwood detected in urine, may indicate that this oil works on the urinary system while garlic's components are detected with the out-breath. It is very interesting that one essential oil appears to naturally find one method of getting out of the body, while another oil finds another route. It may well be that all oils are excreted in all the usual manners, but to differing degrees in each.

When using essential oils on the body, whether as a massage oil or in baths, we are still utilizing the nasal/olfactory route, due to the fact that aromatic molecules are volatile and float around in the air as we receive a massage or take the bath. Also, depending on the particular method used, other routes of entry may be involved. Let us look briefly at these methods of entry in detail, and speculate on how the essential oils may work.

The Sense of Smell

Our brain responds to smells very quickly because our life may depend on it. When smoke from another room reaches our nose and our brain responds by saying, "Fire!" we leap up and rush to attend to it. Smells warn us when food is bad or danger is near. The brain also responds to good smells — babies snuggle into their mothers' familiar breasts. Recognizing the smell and knowing safety and food are near, they relax and fall asleep. As children we build up a memory bank of aromas, some of which have good connotations, and some bad. If home life was happy and Mother baked pies with cinnamon, the aroma of that spice will, in later life, evoke memories of times spent happily around the kitchen table. If a child was looked after by indifferent parents who wore lemon-scented perfumes, that aroma could, in later life, bring back uncomfortable, perhaps vague, memories and the aroma will be avoided. In this way, each of us develops an individual aroma history, which continues to develop with time.

Over and above our individual histories with aromas, there are certain types of aroma. Classifying these types has proved difficult because the human nose can distinguish between 10,000 different smells, and that indicates there's a very complex mystery for science to unravel. As of this writing, the exact mechanism for olfaction has not yet been discovered. Some olfactory nerve receptors have been identified, but the process has not been observed experimentally. We know proteins are involved and that, basically, the aroma molecules set off reactions in the brain. The connection is as follows: the aroma molecule hits receptors on small hairlike cilia which extend downwards from the two olfactory bulbs, spoonlike protrusions which are part of the brain. These olfactory bulbs give us our most direct and quickest access to the brain — through aroma.

The part of the brain that most directly responds to olfactory stimulus is the limbic system, which corresponds to our feelings, memories, stored learned responses, and emotions. The limbic system is the most ancient part of the brain, the central core over which the cerebral cortex lies. When aromatic messages reach the limbic system, they are processed instantly and instinctively. This is why aromas are so powerful. They can make us behave in particular ways, without us even knowing what we are doing. In an experiment by Dr. Alan Hirsch of the Smell & Taste Treatment and Research Foundation, Chicago, sweet aromas were put around particular gambling machines in Las Vegas and people responded by putting more money in those machines. The management liked the experiment, you can be sure.

Today, olfactory manipulation is far more than an experiment, it is a part of daily life. In banks in Japan, keyboard operators working in large buildings are perked up in the afternoon by the aroma of lemon being diffused into the working environment. The new school of Japanese architecture, which designs for the perfect working environment, recommends commercial diffusion systems capable of diffusing a variety of different aromas into different areas of the workplace, throughout the day. To calm worried relatives, at least one hospital in America has essential oils diffused in the waiting areas. An increasing number of hotels and retail outlets pump both natural and synthetic aromas into the atmosphere to make people relaxed, so they feel like staying longer (or coming back another time) while spending more money. Marketers in the olfaction field are fond of saying that aroma-psychology is the new frontier in the business. (See The Fragrant Mind by Valerie Ann Worwood.)