An essential oil is a concentrated, hydrophobic In chemistry, hydrophobicity is the physical property of a molecule (known as a hydrophobe) that is repelled from a mass of water liquid Liquid is one of the three classical states of matter. Like a gas, a liquid is able to flow and take the shape of a container, but, like a solid, it resists compression. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density. A distinctive property of the liquid state is surface tension, containing volatile aroma compounds An aroma compound, also known as odorant, aroma, fragrance or flavor, is a chemical compound that has a smell or odor. A chemical compound has a smell or odor when two conditions are met: the compound needs to be volatile, so it can be transported to the olfactory system in the upper part of the nose, and it needs to be in a sufficiently high from plants Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004,. Essential oils are also known as volatile or ethereal oils, or simply as the "oil of" the plant from which they were extracted, such as oil of clove. An oil An oil is any substance that is liquid at ambient temperatures and is hydrophobic but soluble in organic solvents. Oils have a high carbon and hydrogen content and are nonpolar substances. The general definition above includes compound classes with otherwise unrelated chemical structures, properties and uses, including vegetable oils, is "essential" in the sense that it carries a distinctive scent, or essence, of the plant. Essential oils do not as a group need to have any specific chemical properties in common, beyond conveying characteristic fragrances. They are not to be confused with essential fatty acids Essential fatty acids, or EFAs, are fatty acids that cannot be constructed within an organism from other components by any known chemical pathways, and therefore must be obtained from the diet. The term refers to fatty acids involved in biological processes, and not those which may just play a role as fuel. As many of the compounds created from.

Essential oils are generally extracted by distillation Distillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction. Other processes include expression, or solvent extraction Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid phase into another liquid phase. Liquid-liquid extraction is a basic. They are used in perfumes Perfume is a mixture of fragrant essential oils and aroma compounds, fixatives, and solvents used to give the human body, animals, objects, and living spaces a "pleasant" smell, cosmetics Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, permanent waves, colored contact lenses, hair colors, hair sprays and gels, deodorants, baby products, bath oils, bubble baths, bath, soap Soap is an anionic surfactant used in conjunction with water for washing and cleaning, which historically comes either in solid bars or in the form of a viscous liquid and other products, for flavoring Seasonings include herbs, spices, which are themselves frequently referred to as "seasonings". However, Larousse Gastronomique states that "to season and to flavour are not the same thing", insisting that seasoning includes a large or small amount of salt being added to a preparation. Salt may be used to draw out water, or to food and drink, and for scenting incense Incense is composed of aromatic biotic materials, which release fragrant smoke when burned. The term incense refers to the substance itself, rather than to the odor that it produces and household cleaning products.

Various essential oils have been used medicinally at different periods in history. Medical application proposed by those who sell medicinal oils range from skin treatments to remedies for cancer, and are often based on historical use of these oils for these purposes. Such claims are now subject to regulation in most countries, and have grown more vague to stay within these regulations.

Interest in essential oils has revived in recent decades with the popularity of aromatherapy Aromatherapy is a form of alternative medicine that uses volatile plant materials, known as essential oils, and similar aromatic compounds from plants, for the purpose of improving a person's mood, cognitive function or health. Preliminary scientific evidence is growing in all these areas. An aroma therapist is the person who performs the, a branch of alternative medicine In Western culture, alternative medicine is any healing practice "that does not fall within the realm of conventional medicine", or "that which has not been shown consistently to be effective." It is often opposed to evidence based medicine and encompasses therapies with a historical or cultural, rather than a scientific, basis which claims that the specific aromas carried by essential oils have curative effects. Oils are volatilized or diluted in a carrier oil and used in massage, diffused in the air by a nebulizer or by heating over a candle flame, or burned as incense, for example.

Production

Distillation

Today, most common essential oils, such as lavender, peppermint, and eucalyptus, are distilled. Raw plant material, consisting of the flowers A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds. The process begins with pollination, is followed by fertilization, leading to the formation and dispersal of the seeds. For, leaves In botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat and thin. There is continued debate about whether the flatness of leaves evolved to expose the chloroplasts to more light or to increase the absorption of carbon dioxide. In either case, the adaption was made at the expense, wood Wood is an organic material; in the strict sense wood is produced as secondary xylem in the stems of trees . In a living tree it transfers water and nutrients to the leaves and other growing tissues, and has a support function, enabling woody plants to reach large sizes or to stand up for themselves. However, wood may also refer to other plant, bark Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner bark, which in older stems is living tissue, includes, roots In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating (growing up above the ground or especially above water). Furthermore, a stem normally occurring below ground is not exceptional either (see rhizome). So, it is, seeds A seed ( /ˈsiːd/ ), referred to as a kernel in some plants, is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant. The formation of the seed completes, or peel Peel, also known as rind or skin, is the outer protective layer of a fruit or vegetable which could be peeled off. The rind is usually the botanical exocarp, but the term exocarp does also include the hard cases of nuts, which are not named peels since they are not peeled off by hand or peeler, but rather shells because of their hardiness, is put into an alembic An alembic is an alchemical still consisting of two retorts connected by a tube. Technically, the alembic is only the upper part (the capital or still-head), while the lower part is the cucurbit, but the word was often used to refer to the entire distillation apparatus. A modern descendant of the alembic (used to produce alcohol) is the pot still (distillation apparatus) over water Water is a ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life. As the water is heated the steam passes through the plant material, vaporizing the volatile compounds. The vapors flow through a coil where they condense back to liquid, which is then collected in the receiving vessel.

Most oils are distilled in a single process. One exception is Ylang-ylang (Cananga odorata Ylang-ylang , Cananga odorata forma genuina , is a small flower of the cananga tree. It is a fast-growing tree that exceeds 5 meters per year and attains an average height of 12 meters. It grows in full or partial sun, and prefers the acidic soils of its native rainforest habitat. The leaves are long, smooth and glossy. The flower is greenish), which takes 22 hours to complete through a fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation. Generally the component parts boil at less than 25 °C from.

The recondensed water is referred to as a hydrosol, hydrolat, herbal distillate Herbal distillates are aqueous solutions or colloidal suspensions of essential oils usually obtained by steam distillation from aromatic plants. These herbal distillates have uses as flavorings, medicine and in skin care. Herbal distillates go by many other names including floral water, hydrosol, hydrolate, herbal water and essential water or plant water essence, which may be sold as another fragrant product. Popular hydrosols include rose water Rose water or rose syrup is the hydrosol portion of the distillate of rose petals. Rose water, itself a by-product of the production of rose oil for use in perfume, is used to flavour food, as a component in some cosmetic and medical preparations, and for religious purposes throughout Europe and Asia, lavender water, lemon balm Lemon balm , not to be confused with bee balm, Monarda species, is a perennial herb in the mint family Lamiaceae, native to southern Europe and the Mediterranean region, clary sage Salvia sclarea, clary, or clary sage, is a biennial herb in the genus Salvia which is native throughout Europe and east and central Asia, but which was historically mostly found in southern France, Italy, Switzerland, and Syria and orange blossom water. The use of herbal distillates in cosmetics Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, permanent waves, colored contact lenses, hair colors, hair sprays and gels, deodorants, baby products, bath oils, bubble baths, bath is increasing. Some plant hydrosols have unpleasant smells and are therefore not sold.

Expression

Most citrus Citrus is a common term and genus of flowering plants in the family Rutaceae, originating in tropical and subtropical southeast regions of the world. The most well known examples are the orange, the lemon, the grapefruit, and the lime. The Latin word citrus was borrowed from ancient Greek kedros "cedar, juniper" probably through Etruscan peel oils are expressed mechanically, or cold-pressed. Due to the relatively large quantities of oil in citrus peel and low cost to grow and harvest the raw materials, citrus-fruit oils are cheaper than most other essential oils. Lemon or sweet orange oils that are obtained as by-products A by-product is a secondary or incidental product deriving from a manufacturing process, a chemical reaction or a biochemical pathway, and is not the primary product or service being produced. A by-product can be useful and marketable, or it can be considered waste of the citrus industry are even cheaper.

Prior to the discovery of distillation, all essential oils were extracted by pressing.

Solvent extraction

Most flowers contain too little volatile oil to undergo expression and their chemical components are too delicate and easily denatured by the high heat used in steam distillation. Instead, a solvent The most common solvent in everyday life is water. Most other commonly-used solvents are organic chemicals. These are called organic solvents. Solvents usually have a low boiling point and evaporate easily or can be removed by distillation, leaving the dissolved substance behind. To distinguish between solutes and solvents, solvents are usually such as hexane Hexane is an hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms. The term may refer to any of five structural isomers with that formula, or to a mixture of them: or supercritical carbon dioxide Supercritical carbon dioxide refers to carbon dioxide that is in a fluid state while also being at or above both its critical temperature and pressure, yielding rather uncommon properties. Carbon dioxide usually behaves as a gas in air at STP or as a solid called dry ice when frozen. If the temperature and pressure are both increased from STP to is used to extract the oils. Extracts from hexane and other hydrophobic solvent are called concretes, which is a mixture of essential oil, waxes Wax refers to beeswax or another substance with similar properties. The traditional meaning, beeswax, refers to a substance secreted by bees and used by them in constructing their honeycombs. The term has come to refer more generally to a class of substances with properties similar to beeswax, enumerated below:, resins Resin is a hydrocarbon secretion of many plants, particularly coniferous trees. It is valued for its chemical constituents and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and perfume. Fossilized resins are the source of amber. Resins are also a material in nail polish, and other lipophilic Lipophilicity, , refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true. Thus lipophilic substances tend to dissolve in other lipophilic substances, while (oil soluble) plant material.

Although highly fragrant, concretes contain large quantities of non-fragrant waxes and resins. As such another solvent, often ethyl alcohol Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs. In common usage, it is often referred to simply as, which only dissolves the fragrant low-molecular weight compounds, is used to extract the fragrant oil from the concrete. The alcohol is removed by a second distillation, leaving behind the absolute Similar to essential oils, absolutes are concentrated, highly-aromatic, oily mixtures extracted from plants. Whereas essential oils can typically be produced through steam distillation, absolutes require the use of solvent extraction techniques or more traditionally, through enfleurage.

Supercritical carbon dioxide is used as a solvent in supercritical fluid extraction. This method has many benefits, including avoiding petrochemical Petrochemicals are chemical products made from raw materials of petroleum or other hydrocarbon origin. Although some of the chemical compounds that originate from petroleum may also be derived from other sources such as coal or natural gas, petroleum is a major source of many. This article is mainly intended to discuss organic compounds or residues in the product and the loss of some "top notes" when steam distillation is used. It does not yield an absolute directly. The supercritical carbon dioxide will extract both the waxes and the essential oils that make up the concrete. Subsequent processing with liquid carbon dioxide, achieved in the same extractor by merely lowering the extraction temperature, will separate the waxes from the essential oils. This lower temperature process prevents the decomposition and denaturing of compounds. When the extraction is complete, the pressure is reduced to ambient and the carbon dioxide reverts back to a gas, leaving no residue. An animated presentation describing the process is available for viewing.

Supercritical carbon dioxide is also used for making decaffeinated coffee Decaffeination is the act of removing caffeine from coffee beans, mate, cocoa, tea leaves and other caffeine-containing materials. However, although it uses the same basic principles it is a different process because of the difference in scale.

Production quantities

Estimates of total production of essential oils are difficult to obtain. One estimate, compiled from data in 1989, 1990 and 1994 from various sources gives the following total production, in tonnes, of essential oils for which more than 1,000 tonnes were produced.^[1]

Oil	Tonnes
Sweet orange An orange—specifically, the sweet orange—is the citrus Citrus ×sinensis and its fruit. The orange is a hybrid of ancient cultivated origin, possibly between pomelo (Citrus maxima) and tangerine (Citrus reticulata). It is a small flowering tree growing to about 10 m tall with evergreen leaves, which are arranged alternately, of ovate shape	12,000
Mentha arvensis Mentha arvensis is a species of mint with a circumboreal distribution. It is native to the temperate regions of Europe and western and central Asia, east to the Himalaya and eastern Siberia, and North America	4,800
Peppermint Peppermint is a hybrid mint, a cross between the watermint (Mentha aquatica) and spearmint (Mentha spicata). The plant, indigenous to Europe, is now widespread in cultivation throughout all regions of the world. It is found wild occasionally with its parent species	3,200
Cedarwood Cedar is a genus of coniferous trees in the plant family Pinaceae. They are most closely related to the Firs (Abies), and share a very similar cone structure. They are native to the mountains of the western Himalaya and the Mediterranean region, occurring at altitudes of 1,500–3,200 m in the Himalaya and 1,000–2,200 m in the Mediterranean	2,600
Lemon The lemon is a small evergreen tree originally native to Asia, and is also the name of the tree's oval yellow fruit. The fruit is used for culinary and nonculinary purposes throughout the world – primarily for its juice, though the pulp and rind (zest) are also used, mainly in cooking and baking. Lemon juice is about 5% (approximately 0.3 mole	2,300
Eucalyptus globulus	2,070
Litsea cubeba	2,000
Clove (leaf)	2,000
Spearmint	1,300

Use in aromatherapy

Aromatherapy is a form of alternative medicine, in which healing effects are ascribed to the aromatic compounds in essential oils and other plant extracts. Many common essential oils have medicinal properties that have been applied in folk medicine since ancient times and are still widely used today. For example, many essential oils have antiseptic properties.^[2] Many are also claimed to have an uplifting effect on the mind. The claims are supported in some studies^[3][4] and unconfirmed in others.^[5]

Dilution

Essential oils are usually lipophilic (literally: "oil-loving") compounds that usually are not miscible with water. Instead, they can be diluted in solvents like pure ethanol (alcohol), polyethylene glycol, or oils.

Raw materials

Essential oils are derived from various sections of plants. Some plants, like the bitter orange, are sources of several types of essential oil.

Berries Allspice Juniper Seeds Almond Anise Celery Cumin Nutmeg oil Bark Cassia Cinnamon Sassafras Wood Camphor Cedar Rosewood Sandalwood Agarwood Rhizome Galangal Ginger

Leaves Basil Bay leaf Cinnamon Common sage Eucalyptus Lemon grass Melaleuca Oregano Patchouli Peppermint Pine Rosemary Spearmint Tea tree Thyme Wintergreen Resin Frankincense Myrrh

Flowers Cannabis Chamomile Clary sage Clove Scented geranium Hops Hyssop Jasmine Lavender Manuka Marjoram Orange Rose Ylang-ylang Peel Bergamot Grapefruit Lemon Lime Orange Tangerine Root Valerian

Rose oil

The most well-known essential oil is probably rose oil, produced from the petals of Rosa damascena and Rosa centifolia. Steam-distilled rose oil is known as "rose otto" while the solvent extracted product is known as "rose absolute".

Dangers

Because of their concentrated nature, essential oils generally should not be applied directly to the skin in their undiluted or "neat" form. Some can cause severe irritation or provoke an allergic reaction. Instead, essential oils should be blended with a vegetable-based "carrier" oil (a.k.a., a base, or "fixed" oil) before being applied. Common carrier oils include olive, almond, hazelnut and grapeseed. Only neutral oils should be used. A common ratio of essential oil disbursed in a carrier oil is 0.5–3% (most under 10%), depending on its purpose. Some essential oils, including many of the citrus peel oils, are photosensitizers, increasing the skin's vulnerability to sunlight. Industrial users of essential oils should consult the material safety data sheets (MSDS) to determine the hazards and handling requirements of particular oils.

Gynecomastia

Estrogenic and antiandrogenic activity have been reported by in vitro study of tea tree oil and lavender essential oils. Case reports suggest that the oils may be implicated in some cases of gynecomastia, an abnormal breast tissue growth, in prepubescent boys.^[6][7]

Pesticide residues

There is some concern about pesticide residues in essential oils, particularly those used therapeutically. For this reason, many practitioners of aromatherapy buy organically produced oils.

Ingestion

While some advocate the ingestion of essential oils for therapeutic purposes, this should never be done except under the supervision of someone licensed to prescribe such treatment. Some common essential oils such as Eucalyptus are toxic internally. Pharmacopoeia standards for medicinal oils should be heeded. Some oils can be toxic to some domestic animals, cats in particular.^[8] The internal use of essential oils can pose hazards to pregnant women, as some can be abortifacients in dose 0.5–10 ml.

Flammability

The flash point of each essential oil is different. Many of the common essential oils such as tea tree, lavender, and citrus oils are classed as a Class 3 Flammable Liquid as they have a flash point of 50–60 °C.

Toxicology

LD₅₀ of most essential oils or their main components are 0.5–10 mg/kg (orally or skin test).^{[citation needed]} This compares with, for example, the LD₅₀ of arsenic acid, one of the most common arsenic based poisons which is 6 mg/kg (rabbits).^[9]

Standardization of its derived products

In 2002, ISO published ISO 4720 in which the botanical names of the relevant plants are standardized ^[10]. The rest of the standards with regards to this topic can be found in the section of ICS 71.100.60 ^[11]

Industrial resources

• Flavour and Fragrance Journal ^[12]
• Journal of Essential Oil Research ^[13]

Notes and references

1. ^ "ISO TC 54 Business Plan — Essential oils" (PDF). http://isotc.iso.org/livelink/livelink/971087/ISO_TC_054__Essential_oils_.pdf. Retrieved 2006-09-14. It is unclear from the source what period of time the quoted figures include.
2. ^ Seenivasan Prabuseenivasan, Manickkam Jayakumar, and Savarimuthu Ignacimuthu (November 30, 2006). "In vitro antibacterial activity of some plant essential oils". BMC Complement Altern Med. 6: 39. doi:10.1186/1472-6882-6-39. PMID 17134518. PMC 1693916. http://www.biomedcentral.com/1472-6882/6/39.
3. ^ Komiya M, Takeuchi T, Harada E (September 25, 2006). "Lemon oil vapor causes an anti-stress effect via modulating the 5-HT and DA activities in mice". Behav Brain Res 172 (2): 240–9. doi:10.1016/j.bbr.2006.05.006. PMID 16780969. http://linkinghub.elsevier.com/retrieve/pii/S0166-4328(06)00279-8. Retrieved 2006-12-24.
4. ^ Hiroko Kuriyama, Satoko Watanabe, Takaaki Nakaya, Ichiro Shigemori, Masakazu Kita, Noriko Yoshida, Daiki Masaki, Toshiaki Tadai, Kotaro Ozasa, Kenji Fukui, and Jiro Imanishi (September 15, 2005). "Ambient odors of orange and lavender reduce anxiety and improve mood in a dental office". Physiol Behav 86 (1-2): 92–5. doi:10.1016/j.physbeh.2005.06.031. PMID 16095639.
5. ^ Lehrner J, Marwinski G, Lehr S, Johren P, Deecke L (June 2005). "Immunological and Psychological Benefits of Aromatherapy Massage". Evid Based Complement Alternat Med 2 (2): 179. doi:10.1093/ecam/neh087. PMID 15937558.
6. ^ Henley, D. V. (2007). "Prepubertal gynecomastia linked to lavender and tea tree oils". New England Journal of Medicine 356 (5): 479–85. doi:10.1056/NEJMoa064725. PMID 17267908.
7. ^ "Oils make male breasts develop". BBC News. 2007-02-01. http://news.bbc.co.uk/2/hi/health/6318043.stm. Retrieved 2007-09-09.
8. ^ Bischoff K, Guale F (April 1998). "Australian tea tree (Melaleuca alternifolia) oil poisoning in three purebred cats". J. Vet. Diagn. Invest. 10 (2): 208–10. PMID 9576358. http://www.jvdi.org/cgi/pmidlookup?view=long&pmid=9576358.
9. ^ Joachimoglu. Biochem. Z. 70, 144 (1915)
10. ^ International Organization for Standardization. "ISO 4720:2002 Essential oils — Nomenclature". http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?ics1=01&ics2=040&ics3=71&csnumber=30435. Retrieved 23 April 2009.
11. ^ International Organization for Standardization. "71.100.60: Essential oils". http://www.iso.org/iso/products/standards/catalogue_ics_browse.htm?ICS1=71&ICS2=100&ICS3=60&. Retrieved 14 June 2009.
12. ^ John Wiley & Sons. "Flavour and Fragrance Journal". http://www3.interscience.wiley.com/journal/4029/home. Retrieved 11 July 2009.
13. ^ Allured Business Media. "Journal of Essential Oil Research". http://www.jeoronline.com/. Retrieved 11 July 2009.

Additional references

• Kurt Schnaubelt (1999). Advanced Aromatherapy: The Science of Essential Oil Therapy. Healing Arts Press. ISBN 0-89281-743-7.
• Wanda Sellar (2001). The Directory of Essential Oils (Reprint ed.). Essex: The C.W. Daniel Company, Ltd. ISBN 0-85207-346-1.
• Robert Tisserand (1995). Essential Oil Safety: A Guide for Health Care Professionals. Churchill Livingstone. ISBN 0-443-05260-3.

See also

• Alternative medicine
• Aromatherapy
• Enfleurage
• Fragrance oil
• List of essential oils
• List of vegetable oils
• Volatility (chemistry)

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