International Centre for Science and High Technology

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International Centre for
Science and High Technology

United Nations Industrial
Development Organization



Anadolu University

Faculty of Pharmacy

Department of Pharmacognosy

26470 Eskisehir


Presented at the Expert Group Meeting on Priority Needs of Developing Countries in the Field of MAPS held in Trieste, Italy, 21 – 22 February 2011


Essential oils are mixtures of volatile chemicals found in natural matrices. They are responsible for the odour and sometimes taste properties of aromatic materials which may be of plant, animal or microbial origin. They are produced by organisms found in terrestrial and marine realms. They are variously found in glandular hairs, glands, secretory cells, secretory ducts or cavities, etc. depending on their origin. Aromatic plants are the major source of essential oils and they may be found in almost all parts of a plant such as leaves, flowers, bark, seeds, fruits, wood, root, root bark. Among many orhers, main essential oil plant bearing families include Apiaceae, Lamiaceae, Asteraceae, Cupressaceae, Lauraceae, Pinaceae, Rutaceae, Myrtaceae, Santalaceae, Zingiberaceae, Zygophyllaceae, etc. In some plant families, essential oil components contained in various organs are bound with sugars to form glycosides which are not volatile. They can be volatilized by enzymatic or chemical hydrolysis. A few of them are found in animal sources such as musk, civet or sperm whale, or produced by microorganisms. Production of essential oils from animals has been banned in order to protect biodiversity. Mosses, liverworts, lichens, seaweeds, sponges, fungi and insects have also been shown to biosynthesize essential oils. Essential oils are frequently associated with gums and/or resins. They are freed from such products by distillation. The Council of Europe describes essential oil as a product obtained from vegetable raw material.

Due to their liquid nature at room temperature, essential oils are called oils. However, they should not be confused with fixed or fatty oils, which comprise naturally occurring mixtures of lipids which may not necessarily be volatile. Therefore, essential oils differ entirely from fixed oils both in chemical and in physical properties. A simple test can verify the occurrence of an essential oil. When dropped on a filter paper, essential oil evaporates completely; however, fixed oil leaves a permanent stain which does not evaporate even when heated.

Essential oils can be freed from their matrices by a thermal process or expression and are obtained by water or steam distillation, dry distillation, or expression only in the case of citrus fruits. Aromatic chemicals can be captured from the headspace of plant parts emitting volatiles by headspace trapping techniques. Aromatic materials can also be recovered by extracting with organic solvents or fluidized gasses but the resulting material is not technically considered an essential oil. Concretes, absolutes, spice oleoresins, etc. are considered aromatic extracts which contain non-volatile components as well.

Essential oils are composed of volatile hydrocarbons and their derivatives containing O, N, S in their formulae. Marine organisms may also yield oil components containing halogens. Alkanes, alkenes, benzenoids, phenylpropanoids, terpenoids (e.g., mono-, sesqui-, diterpenes), fatty acids and their esters, macrocyclic lactones, coumarins, phthalides, isothiocyanates are the groups of components found in essential oils. They may exist in the form of alcohols, acids, esters, epoxides, aldehydes, ketones, amines, sulphides, etc.

Essential oils, their fractions and isolated aroma chemicals are valuable ingredients of flavour and fragrance, food, perfumery, cosmetics and toiletries, fine chemicals, and pharmaceutical industries, and are utilized as such or in diluted forms in therapy or by the aromatherapy sector.

The function of essential oil in plants is not fully understood. Microscopic examination of plant parts that contain the oil sacs readily shows their presence. The odours of flowers are said to act as attractants for insects involved in pollination and thus may aid in preservation and natural selection. Essential oils are almost always bacteriostats, often bacteriocides and antimicrobials having a wide range activity spectrum. Many chemicals of essential oils are active and thus could participate readily in metabolic reactions. They are sources of plant metabolic energy, although some chemists have referred to them as waste products of plant metabolism. Exudates, which contain essential oils, e.g, balsams and resins, act as protective seals against disease or parasites, prevent loss of sap, and are formed readily when the tree trunks are damaged.


Essential oils are produced from dry or fresh plant materials by distillation. Citrus oils are the only essential oils obtained by cold pressing. Various technologies have been developed for their production. Dry distillation is a thermal degradation process in order to obtain tar such as birch, cade, pine and cedar tars. This process involves applying intense heat to scrap wood material from the top in totally anaerobic condition. Due to thermal degradation, a viscous dark coloured, tarry liquid with smoky odour separates and collects in a container underneath the vessel. This material separates into two layers in 15-20 days. Tar sinks to the bottom of the water layer and the oil floats on top. It contains methanol, acetic acid and degradation products of lignin.

The following techniques are more commonly used for the distillation of essential oils:

Water distillation (Hydrodistillation)

This technique involves boiling plant material in water. Volatiles evaporating alongside water vapour condense on the surface of a cooled condenser and collect at a collecting vessel (Florentine flask). Due to insolubility in water essential oil floats on top or sinks to the bottom according to its density. Rose oil is obtained by water distillation. Laboratory scale essential oil distillation equipment (Clevenger apparatus) operates on this principle.

Steam distillation

Plant materials are packed in a perforated basket or on a perforated plate and steam generated outside is fed from the bottom in a closed vessel. Steam carries away the essential oil on the plant material. Condensed water and oil separate due to density differences. This is the most popular essential oil distillation technique favoured by the industry.

Water and steam distillation

Water and steam distillation is similar to Steam distillation, however, in this technique, steam is generated at the bottom of the vessel below a perforated plate. This is the favoured technique by the cottage industry.

Cohobation is a technique applied during water and water and steam distillation processes. It involves feeding of the distillate water back into the still during distillation. Aim is to reduce the loss of phenolics and other oxygenated compounds to a minimum.

Cohobation is also applied in rose oil distillation. In a cohobation still, distillate waters are continuously fed into the vessel to improve the yield of oil. In rose oil distillation, distillate waters are redistilled in another still to get more oil. At the end of the season, this oil rich in phenylethyl alcohol is mixed with the first oil to produce the Turkish rose oil.

Mobile distillation is a steam distillation technique applied in a large farm cultivating aromatic plants (e.g., mint, lavender, etc.). Mechanically harvested and wilted (if necessary) plant material is packed in large (8 tons) stills on wheels and pulled to a central distillation facility where a steam generator, condensers and a collecting vessel are placed. Steam is plugged into the still and condensate line is also arranged through appropriate hoses. Each mobile distillation facility can dock multiple stills (up to 8 app.) and the condensates from all stills are directed to the same collecting vessel. Stills are unloaded and sent back to the field for further loading.

Endless screw type stills are used for continuous distillation especially in Russia to produce fennel, pine, juniper oils and ethanol from fermented grapes for the last half a century and also in the USA for cedarwood oil distillation. In this system, while finely powdered plant material slowly moves downwards countercurrent steam liberates and carries away the oil, which is condensed and collected in the usual way.

Hydrodiffusion is a steam distillation method, whereby steam is fed to the plant material from the top. Steam penetrating the plant matrix condenses and forces the essential oil to diffuse to the surface. Due to forces of gravity, oil leaves the vessel together with the condensate water from the bottom of the still. Powdered material results in better oil yields. The disadvantage of this technique is the undesired extraction of coumarins, psoralens, chlorophyll into the oil. Therefore, hydrodiffusion has not become a widely used distillation technique.

Rectified oils have been redistilled to improve a particular property or characteristic, such as flavour or aroma. For example, natural oil of peppermint is frequently rectified to remove dimethyl sulfide, which has a powerful and objectionable cooked vegetable note deleterious to the use of the oil in Creme de Menthe liqueurs. Distillation is also used to remove psoralens, which are harmful photosensitizing agents present in natural bergamot oil. Colour may be removed, e.g. from cassia oil, by vacuum steam distillation. A desirable component, such as 1,8-cineole (eucalyptol) 85% in eucalyptus oil, may be concentrated further by distillation to remove a forerun (topping).

Concentrated or folded oils are processed by various physical means to remove wholly or partly undesirable or non-flavor components, such as terpenes or sesquiterpenes, which have poor alcohol and water solubility, very low flavor value, and poor stability. Although this group, for the most part, comprises citrus oils with high terpene contents which cause clouding in drink applications, other oils such as spearmint are included. The processing methods include fractional distillation, topping, solvent extraction, countercurrent extraction, supercritical extraction, thin-film evaporation, and molecular distillation. In some cases, both distillation and solvent extraction are needed for complete removal of terpenes. Thus, such oils as tangerine-terpeneless, lemon-sesquiterpeneless, or orange-80% terpeneless are processed oils. Some oils, particularly citrus, are folded or concentrated to reduce the terpene content to a designated level, i.e., when half of the volatile constituents of the oil are removed, their removal is said to double the concentration and the oil is then called twofold. Although termed concentration, this process is, nevertheless, not merely a concentration in the ordinary sense, since the flavour body of the concentrate is always weaker than that of the complete essential oil, demonstrating that valuable products are lost in the course of removing the terpenes. In the past, a distinction was made between terpeneless and sesquiterpeneless oils, but this distinction has been abandoned since it is only fractional distillation, which can practically remove monoterpenes without removing sesquiterpenes at the same time.

The choice of extraction technique depends upon the material to be extracted, essential oil yield and quality, and marketability of the product. More recent extraction techniques using fluidized gasses [e.g., supercritical carbondioxide (SFE), phytosol] maybe preferred to the classical solvent extraction techniques.

Essential oils are primarily analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) for component analysis and quantification of its complex mixture of constituents. For quality control, requirements in monographs published by standards organizations and pharmacopoeias are followed. European Pharmacopoeia 7th Edition (2010) contains monographs on 31 essential oils used for pharmaceutical purposes.

Biological activities of essential oils and aromachemicals

Aromatherapy is the use of natural essential oils and aromachemicals in therapy. One school of thought considers aromatherapy as “smell therapy” meaning effects are caused only by inhalation. However, in actuality, aromatherapy has been practiced in various forms ranging from inhalation therapy to massaging with oils and even oral consumption of aromatic waters. It may be more appropriate to call this form of therapy as “essential oil therapy” or “therapy with essential oils”. Aromachology is a term often used to describe the physiological effects of scents.

The most popular forms of practice of aromaterapy are as follows:

Oil lamp, oil burner or diffuser: vaporizing essential oils in a small cup heated by a candle.

Inhalation: Inhaling essential oil vapours dropped in hot water.

Bath: adding essential oils to a bathtub before entering.

Massage: diluting essential oils in a vegetable or mineral oil before rubbing on skin.

Aromatherapy is used to treat a range of disorders including digestive problems, skin diseases (e.g., eczema, etc), headaches, insomnia, stress, cancer and for improving cognition. The effects of essential oils and aromachemicals on the nervous system, gastrointestinal system, immune system, respiratory system, antimicrobial and antifungal activities have in recent years been scientifically investigated.

Studies concerning the influence of essential oils and aromachemicals on the nervous system have been carried out. These studies have provided proof to the practice of aromatherapy and more significantly to the efficacy of essential oils or their components in conventional therapy.

Lavender oil and its components linalool and linalyl acetate have been shown to have sedative effects on both animals and human beings in a dose dependent manner.

In studies using Electroencephalographs (EEC) on the use of inhaled compounds -wave dominancy refers to a relaxed state and -wave dominancy to stimulation.

Lavender oil, sandalwood oil and apple aroma induced sedation as evidenced by -wave dominancy, while jasmine odour increased -wave activity hence induced stimulation.

In an experiment with healthy volunteers R-(-)-, S-(+) and racemic linalool were tested. R-(-)-linalool found in lavender oil and the racemic mixture both showed sedative activity. S-(+)-linalool which is obtained from coriander oil, however, showed the reverse.

Lavender oil positively affected mood by inducing a less depressed mood, and more relaxed feeling. Anxiety reduction was better. Better performance was observed in mathematical computations.

In another study to test the olfactive influence of learning, essential oils of lavender, jasmine, sage and rosewood were tested on 160 elementary school children at 3rd and 4th class. Significantly better learning results were obtained with lavender oil on anxious children due to sedating and stress reducing effect of its aroma. No significant results were obtained with the other tested oils. However, jasmine odour yielded rather worse learning results with lethargic children possibly due to stimulating effect of jasmine odour.

Lavender oil vapour and linalool significantly and dose dependently induce anticonvulsive effect. This is possibly due to potentiation of GABAA receptors. Lavender oil, lavender perfumes, leaf alcohol, hinokitol, pinene, eugenol, citronellol and citronellal bind at low concentrations (10-30 M) to the potentiation site of GABAA receptors and increase the affinity of GABA to the receptors. Potentiation of GABAA receptors by benzodiazepine, barbiturate, steroids and anesthesics induce anxiolytic, anticonvulsant and sedative activities.

In another experiment to clarify the anticonvulsant mechanism of linalool, its effects on binding of an NMDA antagonist (MK801) and a GABAA agonist (muscimol) to mouse cortical membranes showed a dose dependent non-competitive inhibition on the antagonist binding but no effect on agonist binding suggesting a direct interaction with the NMDA receptor complex inducing anticonvulsant activity.

Pharmacokinetic basis of the anticonvulsant properties of linalool on glutamate binding sites were investigated. Linalool inhibits by means of competitive antagonism glutamate binding at CNS-membranes delaying NMDA and blocking quinolinic acid induced convulsions. It also inhibits the binding of glutamate to brain cortical membranes and significantly reduces K+-stimulated glutamate release and glutamate uptake but does not interfere with basal glutamate release. These experiments provide proof that linalool can be considered as a promising antiepileptic drug.

A diagnostic method has been developed in brain research using linalool to determine the existence of unilateral supratentorial brain tumors.

Hipnotic or sleep promoting effects of lavender, lavender oil and linalool have been shown both in animals and human beings. Local anesthetic effects of linalool were demonstrated. Lavender flowers are used against states of restlessness, uneasiness, nervousness, difficulties in falling a sleep and anxiety. Lavender tea is taken as a sedative and to promote sleep. Lavender bath relieves stress of the day and brings about calmness and relaxation. Lavender pillows are recommended for difficulties in falling a sleep and for relaxation. Lavender oil is sedative, antistress, relaxant and sleep promoter.

The use of lavender straw as bedding appeared to decrease incidence and severity of travel sickness, symptoms of travel sickness and stress such as retching, vomitting, foaming and chomping appeared to be less acute in pigs.

Lavender and lavender oil showed only very mild skin irritation and sensitisation effects in man, although allergenic reactions were observed in some laboratory animals. In a placebo controlled study, aromastream of lavender was tested against severe dementia in Alzheimer patients suffering from vascular dementia. Sixty percent of the patients showed modest efficacy, sedation and calming.

Fragrance inhalation on sympathetic activity by normal adults was investigated. Inhalation of pepper, estragon, fennel or grapefruit oils resulted in 1.5 to 2.5-fold increase in relative sympathetic activity representing low frequency amplitude of systolic blood pressure (SBP-LF amplitude) compared with an odourless solvent. In contrast, fragrance inhalation of rose oil or patchouli oil caused 40% decrease in relative sympathetic activity. Pepper oil induced a 1.7-fold increase in plasma concentration compared with the resting state, while rose oil caused a 30% decrease in adrenaline concentration.

Anticancer effects

Consumption of diets containing fruits and vegetables rich in monoterpenes such as d-limonene reduces the risk of developing cancer of the colon, mammary gland, liver, prostate and lung. Limonene, perillyl alcohol, geraniol, carveol, farnesol, nerolidol, citronellol, linalool, carvacrol and menthol have shown experimental evidence for the inhibition of induced tumors. Geraniol has been shown to sensitize human colon cancer cells to 5-fluorouracil treatment.

Mechanisms of action against cancer include inhibition of farnesyl transferase (perilla alcohol), increase of pro-apoptotic protein leading to apoptosis of tumor cells (perilla alcohol), protein prenylation (nerolidol).

Antimicrobial effects

Recent studies have shown that the so-called superbugs – pathogenic microorganisms resistant to antibiotics such as MRSA – methicillin-resistant Staphylococcus aureus) cannot survive in the presence of essential oils, nor has there been any pathogen known to resist essential oils by mutating. This may well be due to the fact that bacteria are able to develop genetic mutation and resistance only against a specific drug such as methicillin. But their genetic system seems not to be able to develop defensive mutation versus many natural antibacterial terpenes, such as those found in essential oils. Due to the fact that several hundreds of terpenic compounds may exist in an essential oil and their concentrations may vary due to various reasons, all such variances make impossible the triggering of those genetic mechanisms which on the contrary are successful when they are targeted by a single specific chemical.

It is also known that essential oils are more active against fungi than bacteria. Monoterpenes act on microorganisms through the following mechanisms:

  • Inhibition of the respiration of membranes

  • Increase of permeability of membranes – including K+ leakage

  • Loss of chemiosmotic control leading to the death of bacterium or yeast cell

  • Essential oils are important for food preservation and also for their therapeutic effects on bacterial infections, fungal diseases, wounds, burns, acne, etc. Tea tree oil ex Melaleuca alternifolia (Myrtaceae) containing 32-45% terpinen-4-ol is effective against many gram + and gram – pathogens. Terpinen-4-ol alone has been shown to be more active

In a recent study, 96 essential oils and 23 oil components were tested for antibacterial activity on several strains of four common pathogenic bacteria: Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, Salmonella enterica. The study stemmed from the need to find a comparable method to prove antibacterial activity of the tested material since the literature is full of information on materials tested in a plethora of different methods. Twentyseven oils and 12 compounds were active against all the species of bacteria.

Both the aldehydes (e.g., cinnamaldehyde, citral, citronellal, perillaldehyde, salicylaldehyde) and phenols (e.g., carvacrol, eugenol, isoeugenol, thymol) were found to be very active in bactericidal assays. Monoterpenes with an exocyclic double bond (eugenol and estragol) were generally more active than the isomers with endocyclic double bonds (anethole and isoeugenol).

Anticandidal effects

Candida infections, also called yeast infections, are difficult to deal with due to the paucity of effective cure. Therefore, extensive research is conducted in this field. The difference between antibacterial antibiotics and antifungal agents can be explained by the difference between prokaryote bacteria and eukaryote fungi and yeasts.

Since humans and other mammals have eukaryotic origin like the fungi, it is not so easy to develop a mechanism to inhibit fungal and yeast infections without damaging human cells. This is the reason why there are more antibiotics than antifungal agents.

The difference between mammals and fungi lies in their t-RNA-AA-acyltransferases, steroid synthesize systems (while cholesterol is the main steroid in mammals, it is replaced by ergosterol in fungi) and carbohydrate structure of the cell walls. An added difficulty in developing anticandidal remedies is due to the fact that Candida albicans is a yeast found naturally in the gut flora.

According to AMICBASE database 103.425 data exist on antimicrobial activity of nearly 6000 compounds and over 2000 microorganisms covering the period 1987-1999. In the database over 49.000 data exist on antifungal compounds and 6083 data relate to anticandidial compounds.

Polygodial, a sesquiterpene dialdehyde from Polygonum hidropiper showed stronger activity than the synthetic antifungal agent ketokonazol (MIC 62.5 g/mL). A 32 fold increase in anticandidal activity was obtained when polygodial was used together with trans-anethole, a anticandidal phenylpropanoid from Pimpinella anisum (Anise). Similar enhancement of activity was observed with warburganal, another anticandidial sesquiterpene dialdehyde from Warburgia ugandensis with trans-anethole.

Table 1. Anticandidal activities of compounds in mixtures


MIC (g/mL)



Polygodial + trans-Anethole




Warburganal + trans-Anetole



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