An essential oil is a concentrated

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...

liquid containing volatile (easily evaporated at normal temperatures)

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

s from

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

s. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the oil of the plant from which they were extracted, such as

oil of clove Oil of clove, also known as clove oil, is an essential oil extracted from the clove plant, ''Syzygium aromaticum''. Clove oil is commonly used in aromatherapy and for flavoring food and some medicines. Madagascar and Indonesia are the main produce ...

. An essential

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

is essential in the sense that it contains the essence of the plant's

fragrance An aroma compound, also known as an odorant, aroma, fragrance or flavoring, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently vol ...

—the characteristic fragrance of the plant from which it is derived. The term "essential" used here does ''not'' mean indispensable or usable by the human body, as with the terms

essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life form ...

essential fatty acid Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic ac ...

, which are so called because they are nutritionally required by a living organism. Essential oils are generally extracted by

distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

, often by using steam. Other processes include

expression Expression may refer to: Linguistics * Expression (linguistics), a word, phrase, or sentence * Fixed expression, a form of words with a specific meaning * Idiom, a type of fixed expression * Metaphorical expression, a particular word, phrase, o ...

solvent extraction A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

, ''

sfumatura The ''sfumatura'' or slow-folding process is a traditional technique for manually extracting the essential oils from citrus peel using sponges. Dating back to 18th-century Italy, the process is still carried out in Sicily today, although it is inc ...

'',

absolute Absolute may refer to: Companies * Absolute Entertainment, a video game publisher * Absolute Radio, (formerly Virgin Radio), independent national radio station in the UK * Absolute Software Corporation, specializes in security and data risk manage ...

oil extraction, resin tapping, wax embedding, and cold pressing. They are used in

perfumes Perfume (, ; french: parfum) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and livin ...

cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protect ...

soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...

air fresheners Air fresheners are consumer products that typically emit fragrance and are used in homes or commercial interiors such as restrooms, foyers, hallways, vestibules and other smaller indoor areas, as well as larger areas such as hotel lobbies, auto ...

and other products, for

flavoring A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of the gusta ...

food and drink, and for adding scents to

incense Incense is aromatic biotic material that releases fragrant smoke when burnt. The term is used for either the material or the aroma. Incense is used for aesthetic reasons, religious worship, aromatherapy, meditation, and ceremony. It may also be ...

and household cleaning products. Essential oils are often used for

aromatherapy Aromatherapy is based on the usage of aromatic materials including essential oils and other aroma compounds, with claims for improving psychological and physical well-being. It is offered as a complementary therapy or as a form of alternative m ...

, a form of

alternative medicine Alternative medicine is any practice that aims to achieve the healing effects of medicine despite lacking biological plausibility, testability, repeatability, or evidence from clinical trials. Complementary medicine (CM), complementary and alt ...

in which healing effects are ascribed to aromatic compounds. Aromatherapy may be useful to induce relaxation, but there is not sufficient evidence that essential oils can effectively treat any condition. Improper use of essential oils may cause harm including allergic reactions, inflammation and skin irritation. Children may be particularly susceptible to the toxic effects of improper use. Essential oils can be poisonous if ingested or absorbed through the skin.

Production

Distillation

Most common essential oils such as

lavender ''Lavandula'' (common name lavender) is a genus of 47 known species of flowering plants in the mint family, Lamiaceae. It is native to the Old World and is found in Cape Verde and the Canary Islands, and from Europe across to northern and easte ...

peppermint Peppermint (''Mentha'' × ''piperita'') is a hybrid species of mint, a cross between watermint and spearmint. Indigenous to Europe and the Middle East, the plant is now widely spread and cultivated in many regions of the world.Euro+Med Plantbas ...

tea tree oil Tea tree oil, also known as melaleuca oil, is an essential oil with a fresh camphoraceous odor and a colour that ranges from pale yellow to nearly colourless and clear. It is derived from the leaves of the tea tree, ''Melaleuca alternifolia'', ...

patchouli PatchouliAlso spelled ''patchouly'' or ''pachouli''. (; ''Pogostemon cablin'') is a species of flowering plant in the family Lamiaceae, commonly called the mint or deadnettle family. The plant grows as a bushy perennial herb, with erect stems r ...

, and

eucalyptus ''Eucalyptus'' () is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with several other genera in the tribe Eucalypteae, including '' Corymbia'', they are commonly known as euca ...

are distilled. Raw plant material, consisting of the

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...

, bark,

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...

s, or peel, is put into an

alembic An alembic (from ar, الإنبيق, al-inbīq, originating from grc, ἄμβιξ, ambix, 'cup, beaker') is an alchemical still consisting of two vessels connected by a tube, used for distillation of liquids. Description The complete disti ...

(distillation apparatus) over water. 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 ''Cananga odorata'', known as ylang-ylang ( ) or cananga tree, is a tropical tree that is native to the Philippines, Malaysia, Indonesia, New Guinea, the Solomon Islands, and Queensland, Australia. It is also native to parts of Thailand and Viet ...

'') which is purified through a

fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to ...

. The recondensed water is referred to as a hydrosol, hydrolat,

herbal distillate Herbal distillates, also known as floral waters, hydrosols, hydrolates, herbal waters, and essential waters, are aqueous products of hydrodistillation. They are colloidal suspensions of essential oils as well as water-soluble components obtained ...

, or plant water essence, which may be sold as another fragrant product. Hydrosols include

rose water Rose water ( fa, گلاب) is a flavoured water made by steeping rose petals in water. It is the hydrosol portion of the distillate of rose petals, a by-product of the production of rose oil Rose oil (rose otto, attar of rose, attar of rose ...

water,

lemon balm Lemon balm (''Melissa officinalis'') is a perennial herbaceous plant in the mint family and native to south-central Europe, the Mediterranean Basin, Iran, and Central Asia, but now naturalised elsewhere. It grows to a maximum height of . The l ...

clary sage ''Salvia sclarea'', the clary or clary sage, is a biennial or short-lived herbaceous perennial in the genus ''Salvia''. It is native to the northern Mediterranean Basin, along with some areas in north Africa and Central Asia. The plant has a leng ...

, and

orange blossom water Orange flower Orange flower water, or orange blossom water, is a clear aromatic by-product of the distillation of fresh bitter-orange blossoms for their essential oil. Uses This essential water has traditionally been used as an aromatizer in ...

Expression

Most

citrus ''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...

peel oils are expressed mechanically or cold-pressed (similar to

olive oil extraction Olive oil extraction is the process of extracting the oil present in olive drupes, known as olive oil. Olive oil is produced in the mesocarp cells, and stored in a particular type of vacuole called a lipo vacuole, i.e., every cell conta ...

). 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 are obtained as

byproduct A by-product or byproduct is a secondary product derived from a production process, manufacturing process or chemical reaction; it is not the primary product or service being produced. A by-product can be useful and marketable or it can be consid ...

s of the citrus industry. Before the discovery of distillation, all essential oils were extracted by pressing.

Solvent extraction

Most flowers contain too little volatile oil to undergo expression, but their chemical components are too delicate and easily denatured by the high heat used in steam distillation. Instead, a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

such as

hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...

supercritical carbon dioxide Supercritical carbon dioxide (s) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure. Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as ...

is used to extract the oils. Extracts from

and other hydrophobic solvents are called '' concretes'', which are a mixture of essential oil,

wax Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to giv ...

es,

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on natu ...

s, and other

lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipop ...

(oil-soluble) plant material. Although highly fragrant, concretes contain large quantities of non-fragrant waxes and resins. Often, another solvent, such as

ethyl alcohol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a hyd ...

, is used to extract the fragrant oil from the concrete. The alcohol solution is chilled to for more than 48 hours which causes the

es and

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

s to precipitate out. The precipitates are then filtered out and the ethanol is removed from the remaining solution by evaporation, vacuum purge, or both, leaving behind the ''

''. Supercritical carbon dioxide is used as a solvent in

supercritical fluid A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. It can effuse through porous so ...

extraction. This method can avoid

petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sou ...

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 to a gas, leaving no residue.

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. :

Uses and cautions

Taken by mouth, many essential oils can be dangerous in high concentrations. Typical effects begin with a burning feeling, followed by salivation. Different essential oils may have drastically different pharmacology. Some act as local anesthetic

counterirritant A counterirritant is a substance which creates irritation or mild inflammation in one location with the goal of lessening discomfort and/or inflammation in another location. This strategy falls into the more general category of counterstimulation ...

s and, thereby, exert an

antitussive Cold medicines are a group of medications taken individually or in combination as a treatment for the symptoms of the common cold and similar conditions of the upper respiratory tract. The term encompasses a broad array of drugs, including a ...

(cough suppressing) effect. Many essential oils, particularly

, may cause

contact dermatitis Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes are ...

. Menthol and some others produce a feeling of cold followed by a sense of burning. In Australia essential oils have been increasingly causing cases of poisoning, mostly of children. In the period 2014–2018 there were 4,412 poisoning incidents reported in

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

. *

Use in aromatherapy

Aromatherapy is a form of

in which healing effects are ascribed to the aromatic compounds in essential oils and other plant extracts. Aromatherapy may be useful to induce relaxation, but there is not sufficient evidence that essential oils can effectively treat any condition. Scientific research indicates that essential oils cannot treat or cure any chronic disease or other illnesses. Much of the research on the use of essential oils for health purposes has serious methodological errors. In a systemic review of 201 published studies on essential oils as alternative medicines, only 10 were found to be of acceptable methodological quality, and even these 10 were still weak in reference to scientific standards. Use of essential oils may cause harm including allergic reactions and skin irritation; there has been at least one case of death.

Use as pesticide

Research has shown that some essential oils have potential as a natural

pesticide Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampri ...

. In case studies, certain oils have been shown to have a variety of deterring effects on pests, specifically insects and select arthropods. These effects may include repelling, inhibiting digestion, stunting growth, decreasing rate of reproduction, or death of pests that consume the oil. However, the molecules within the oils that cause these effects are normally non-toxic for mammals. These specific actions of the molecules allow for widespread use of these "green" pesticides without harmful effects to anything else other than pests. Essential oils that have been investigated include rose, lemon grass, lavender, thyme, peppermint, basil, and eucalyptus. Although they may not be the perfect replacement for all synthetic pesticides, essential oils have prospects for crop or indoor plant protection, urban pest control, and marketed insect repellents, such as bug spray. Certain essential oils have been shown in studies to be comparable, if not exceeding, in effectiveness to

DEET ''N'',''N''-Diethyl-''meta''-toluamide, also called DEET () or diethyltoluamide, is the most common active ingredient in insect repellents. It is a slightly yellow oil intended to be applied to the skin or to clothing and provides protection ag ...

, which is currently marketed as the most effective mosquito repellent. Although essential oils are effective as pesticides when first applied in uses such as mosquito repellent applied to the skin, it is only effective in the vapor stage. Since this stage is relatively short-lived, creams and polymer mixtures are used in order to elongate the vapor period of effective repellency. In any form, using essential oils as green pesticides rather than synthetic pesticides has ecological benefits such as decreased residual actions. In addition, increased use of essential oils as pest control could have not only ecological, but economical benefits as the essential oil market diversifies and popularity increases among organic farmers and environmentally conscious consumers. some EOs are authorized, and in use, in the

European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...

: ''

Melaleuca ''Melaleuca'' () is a genus of nearly 300 species of plants in the myrtle family, Myrtaceae, commonly known as paperbarks, honey-myrtles or tea-trees (although the last name is also applied to species of '' Leptospermum''). They range in size ...

'' oil as a

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

citronella oil Citronella oil Citronella oil is an essential oil obtained from the leaves and stems of different species of '' Cymbopogon'' (lemongrass). The oil is used extensively as a source of perfumery chemicals such as citronellal, citronellol, and gerani ...

as a

herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...

, ''

Syzygium aromaticum Cloves are the aromatic flower buds of a tree in the family Myrtaceae, ''Syzygium aromaticum'' (). They are native to the Maluku Islands (or Moluccas) in Indonesia, and are commonly used as a spice, flavoring or fragrance in consumer products, s ...

'' oil as a fungicide and bactericide, ''

Mentha spicata Spearmint, also known as garden mint, common mint, lamb mint and mackerel mint, is a species of Mentha, mint, ''Mentha spicata'' (, native to Europe and southern temperate Asia, extending from Ireland in the west to southern China in the east. I ...

'' oil as a

plant growth regulator Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...

; ''

Citrus sinensis ''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...

'' oil (only in France) for ''

Bemisia tabaci The silverleaf whitefly (''Bemisia tabaci'', also informally referred to as the sweet potato whitefly) is one of several species of whitefly that are currently important agricultural pests. A review in 2011 concluded that the silverleaf whitefly ...

'' on ''

Cucurbita pepo ''Cucurbita pepo'' is a cultivated plant of the genus ''Cucurbita''. It yields varieties of winter squash and pumpkin, but the most widespread varieties belong to the subspecies ''Cucurbita pepo'' subsp. ''pepo'', called summer squash. It has b ...

'' and ''

Trialeurodes vaporariorum ''Trialeurodes vaporariorum'', commonly known as the glasshouse whitefly or greenhouse whitefly, is an insect that inhabits the world's temperate regions. Like various other whiteflies, it is a primary insect pest of many fruit, vegetable and or ...

'' on ''

Solanum lycopersicum The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...

''; and approvals for oils of ''

Thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

'', ''C. sinensis'', and ''

Tagetes ''Tagetes'' () is a genusSoule, J. A. 1996. Infrageneric Systematics of Tagetes. Pgs. 435-443 in Compositae: Systematics, Proceedings of the International Compositae Conference, Kew 1994, Vol. I, Eds. D.J.N. Hind & H.J. Beentje. of annual or ...

'' as insecticides are pending.

Use in food

In relation with their food applications, although these oils have been used throughout history as food preservatives, it was in the 20th century when EOs were considered as Generally Recognized as Safe (GRAS) by the

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...

(FDA). GRAS substances according to the FDA

As antimicrobials

The most commonly used essential oils with antimicrobial action are:

β-caryophyllene Caryophyllene (), more formally (−)-β-caryophyllene, (BCP), is a natural bicyclic sesquiterpene that is a constituent of many essential oils, especially clove oil, the oil from the stems and flowers of ''Syzygium aromaticum'' (cloves), the esse ...

eugenol Eugenol is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds. It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove, nutmeg, cinnamon, basil ...

eugenol acetate Acetyleugenol is a phenylpropanoid compound found in cloves. It is the second in abundance to the related compound eugenol in certain extract preparations. Like eugenol, its found in several plants such as ''Acacia nilotica'' and ''Piper betle'' a ...

carvacrol Carvacrol, or cymophenol, C6H3(CH3)(OH)C3H7, is a monoterpenoid phenol. It has a characteristic pungent, warm odor of oregano. Natural occurrence Carvacrol is present in the essential oil of ''Origanum vulgare'' (oregano), oil of thyme, oil ob ...

linalool Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Linalool has multiple commercial applications, the majority of which are based on its pleasant scent (floral, with a touch of ...

thymol Thymol (also known as 2-isopropyl-5-methylphenol, IPMP), , is a natural monoterpenoid phenol derivative of ''p''-Cymene, isomeric with carvacrol, found in oil of thyme, and extracted from ''Thymus vulgaris'' (common thyme), ajwain, and vario ...

geraniol Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil, palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in water ...

geranyl acetate Geranyl acetate is a monoterpene. It is a colorless liquid with a pleasant floral or fruity rose aroma. It is a colorless liquid but commercial samples can appear yellowish. Geranyl acetate is insoluble in water but soluble in organic solvents. S ...

bicyclogermacrene Germacrenes are a class of volatile organic hydrocarbons, specifically, sesquiterpenes. Germacrenes are typically produced in a number of plant species for their antimicrobial and insecticidal properties, though they also play a role as insect ph ...

cinnamaldehyde Cinnamaldehyde is an organic compound with the formula(C9H8O) C6H5CH=CHCHO. Occurring naturally as predominantly the ''trans'' (''E'') isomer, it gives cinnamon its flavor and odor. It is a phenylpropanoid that is naturally synthesized by the shik ...

geranial Citral is an acyclic monoterpene aldehyde, and being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans' ...

, neral, 1,8-cineole,

methyl chavicol Estragole (''p''-allylanisole, methyl chavicol) is a phenylpropene, a natural organic compound. Its chemical structure consists of a benzene ring substituted with a methoxy group and an allyl group. It is an isomer of anethole, differing with ...

methyl cinnamate Methyl cinnamate is the methyl ester of cinnamic acid and is a white or transparent solid with a strong, aromatic odor. It is found naturally in a variety of plants, including in fruits, like strawberry, and some culinary spices, such as Sichuan p ...

methyl eugenol Methyl eugenol (allylveratrol) is a natural chemical compound classified as a phenylpropene, a type of phenylpropanoid. It is the methyl ether of eugenol and is important to insect behavior and pollination. It is found in various essential oils. ...

camphor Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel ('' Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the k ...

, α-thujone, viridiflorol,

limonene Limonene is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the oil of citrus fruit peels. The -isomer, occurring more commonly in nature as the fragrance of oranges, is a flavoring ag ...

, (''Z'')-linalool oxide,

α-pinene α-Pinene is an organic compound of the terpene class, one of two isomers of pinene. It is an alkene and it contains a reactive four-membered ring. It is found in the oils of many species of many coniferous trees, notably the pine. It is also ...

, ''p''-cymene, (''E'')-caryophyllene, γ-terpinene. Some essential oils are effective

antimicrobials An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...

and have been evaluated for food incorporation

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...

. However, actual deployment is rare because much higher concentrations are required in real foods. Some or all of this lower effectiveness is due to large differences between

culture medium A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Different ...

and foods in: chemistry (especially lipid content), viscosity, and duration of inoculation/storage.

Dilution

Essential oils are usually

(literally: ''"oil-loving"'') compounds that are immiscible (not

miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also applies ...

) with water. They can be diluted in

s like pure

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...

and

polyethylene glycol Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...

Raw materials

Essential oils are derived from sections of plants. Some plants, like the

bitter orange Bitter orange, Seville orange, bigarade orange, or marmalade orange is the citrus tree ''Citrus'' × ''aurantium'' and its fruit. It is native to Southeast Asia and has been spread by humans to many parts of the world. It is probably a cross bet ...

, are sources of several types of essential oil. :

Balsam of Peru

Balsam of Peru Balsam of Peru or Peru balsam, also known and marketed by many other names, is a balsam derived from a tree known as ''Myroxylon balsamum'' var. ''pereirae''; it is found in El Salvador, where it is an endemic species. Balsam of Peru is used i ...

, an essential oil derived from ''

Myroxylon ''Myroxylon'' is a genus of Fabaceae native to Latin America. History The first described species in this genus was '' M. balsamum.'' It was originally described in 1753 by Linnaeus as ''Toluifera balsamum'', based on a specimen collected i ...

'' plants, is used in food and drink for flavoring, in perfumes and toiletries for fragrance, and in animal care products. However, national and international surveys identified balsam of Peru among the "top five" allergens most commonly causing patch test allergic reactions in people referred to

dermatology Dermatology is the branch of medicine dealing with the skin.''Random House Webster's Unabridged Dictionary.'' Random House, Inc. 2001. Page 537. . It is a speciality with both medical and surgical aspects. A dermatologist is a specialist medical ...

clinics.

Garlic oil

Garlic oil Garlic oil is the volatile oil derived from garlic. It is usually prepared using steam distillation and can also be produced via distillation using ether. It is used in cooking and as a seasoning, a nutritional supplement, and also as an insectic ...

is an essential oil derived from

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...

Eucalyptus oil

Most eucalyptus oil on the market is produced from the leaves of ''Eucalyptus globulus''. Steam-distilled eucalyptus oil is used throughout Asia, Africa, Latin America and South America as a primary cleaning/disinfecting agent added to soaped mop and countertop cleaning solutions; it also possesses insect and limited vermin control properties. Note, however, there are hundreds of species of eucalyptus, and perhaps some dozens are used to various extents as sources of essential oils. Not only do the products of different species differ greatly in characteristics and effects, but also the products of the very same tree can vary grossly.

Lavender oil

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Lavender oil has long been used in the production of

perfume Perfume (, ; french: parfum) is a mixture of fragrant essential oils or aroma compounds (fragrances), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agreeable scent. Th ...

. However, studies have shown it can be estrogenic and antiandrogenic, causing problems for prepubescent boys and pregnant women, in particular. Lavender essential oil is also used as an insect repellent.

Rose oil

Rose oil Rose oil (rose otto, attar of rose, attar of roses, or rose essence) is the essential oil extracted from the petals of various types of rose. ''Rose ottos'' are extracted through steam distillation, while ''rose absolutes'' are obtained through ...

is produced from the petals of ''

Rosa damascena Rosa or De Rosa may refer to: People *Rosa (given name) * Rosa (surname) *Santa Rosa (female given name from Latin-a latinized variant of Rose) Places *223 Rosa, an asteroid *Rosa, Alabama, a town, United States *Rosa, Germany, in Thuringia, Ge ...

'' and ''

Rosa centifolia Rosa or De Rosa may refer to: People *Rosa (given name) * Rosa (surname) *Santa Rosa (female given name from Latin-a latinized variant of Rose) Places *223 Rosa, an asteroid *Rosa, Alabama, a town, United States * Rosa, Germany, in Thuringia, G ...

''. Steam-distilled rose oil is known as "rose otto", while the solvent extracted product is known as "rose absolute".

Toxicity

The potential

toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

of essential oil is related to its level or grade of purity, and to the toxicity of specific chemical components of the oil. Many essential oils are designed exclusively for their aroma-therapeutic quality; these essential oils generally should not be applied directly to the skin in their undiluted form. Some can cause severe irritation, provoke an

allergic reaction Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...

and, over time, prove toxic to the liver. If ingested or rubbed into the skin, essential oils can be highly poisonous, causing confusion, choking, loss of muscle coordination, difficulty in breathing,

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...

seizure An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with los ...

s, and possibly severe allergic reactions or

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

. Some essential oils, including many of the

citrus peel Peel, also known as rind or skin, is the outer protective layer of a fruit or vegetable which can be peeled off. The rind is usually the botanical exocarp, but the term exocarp also includes the hard cases of nuts, which are not named peels si ...

oils, are

photosensitizer Photosensitizers produce a physicochemical change in a neighboring molecule by either donating an electron to the substrate or by abstracting a hydrogen atom from the substrate. At the end of this process, the photosensitizer eventually returns to ...

s, increasing vulnerability of the skin to sunlight. Industrial users of essential oils should consult the

safety data sheet A safety data sheet (SDS), material safety data sheet (MSDS), or product safety data sheet (PSDS) is a document that lists information relating to occupational safety and health for the use of various substances and products. SDSs are a widely ...

s to determine the hazards and handling requirements of particular oils. Even certain therapeutic-grade oils can pose potential threats to individuals with epilepsy or pregnant women. Essential oil use in children can pose a danger when misused because of their thin skin and immature livers. This might cause them to be more susceptible to toxic effects than adults.

Flammability

The

flash point The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". (EN 60079-10-1) The fl ...

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

Gynecomastia

Estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

ic and

antiandrogen Antiandrogens, also known as androgen antagonists or testosterone blockers, are a class of drugs that prevent androgens like testosterone and dihydrotestosterone (DHT) from mediating their biological effects in the body. They act by blocking the ...

ic activity have been reported by ''in vitro'' study of

and

essential oils. Two published sets of case reports suggest that lavender oil may be implicated in some cases of

gynecomastia Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Updated by Brent Wisse (1 ...

, an abnormal breast tissue growth in prepubescent boys. The European Commission's Scientific Committee on Consumer Safety dismissed the claims against tea tree oil as implausible, but did not comment on lavender oil. In 2018, a

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...

Production

Distillation

Expression

Solvent extraction

Production quantities

Uses and cautions

Use in aromatherapy

Use as pesticide

Use in food

As antimicrobials

Dilution

Raw materials

Balsam of Peru

Garlic oil

Eucalyptus oil

Lavender oil

Rose oil

Toxicity

Flammability

Gynecomastia

Handling

Ingestion

Pesticide residues

Pregnancy

Toxicology

Standardization of derived products

History

See also

References

Further reading