Essential oils, volatile oils, ethereal oils or aetheroleum are types of oils composed of hydrophobic volatile organic compounds, usually in liquid form, obtained from plant material, such as oil of clove from clove. An essential oil is "essential" in the sense that the oil contains the fragrance or "essence" of that plant. The term "essential" used here does not indicate that it is nutritionally required in the diet, as with essential amino acid or essential fatty acid. A natural component of plant rinds, leaves, or bark, essential oils are fragrant if the plant is crushed or industrially extracted using a steam process.
Essential oils have diverse chemical properties and uses, such as inhalation for aromatherapy or application on skin when diluted for massage. They may be used to lessen pain or exert a cough-suppressing effect.
Many essential oils, particularly tea tree oil, may cause contact dermatitis. Improper use of essential oils may cause harm, including allergic reactions or other adverse effects if ingested, particularly by children.
Production
Essential oils, according to ISO, are produced by steam distillation, by mechanical manipulation of the rind of the fruits of the genus Citrus (also called cold pressing), and by a variety of solvent extraction techniques. An estimated 100,000 tons of essential oils are produced annually (2015). 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. It is unclear from the source what period of time the quoted figures include.
{| class="wikitable" ! Oil !! Tonnes |- | Sweet orange || style="text-align:right;"| 12,000 |- | Mentha arvensis || style="text-align:right;"| 4,800 |- | Peppermint || style="text-align:right;"| 3,200 |- | Cedarwood || style="text-align:right;"| 2,600 |- | Lemon || style="text-align:right;"| 2,300 |- | Eucalyptus globulus || style="text-align:right;"| 2,070 |- | Litsea cubeba || style="text-align:right;"| 2,000 |- | Clove (leaf) || style="text-align:right;"| 2,000 |- | Spearmint || style="text-align:right;"| 1,300
Uses As pesticides Some essential oils have potential as a natural pesticide. 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, cedarwood, 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, 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: Melaleuca oil as a fungicide, citronella oil as a herbicide, Syzygium aromaticum oil as a fungicide and bactericide, Mentha spicata oil as a plant growth regulator; Citrus sinensis oil (only in France) for Bemisia tabaci on Cucurbita pepo and Trialeurodes vaporariorum on Solanum lycopersicum; and approvals for oils of Thymus, C. sinensis, and Tagetes as insecticides are pending.
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 essential oils were considered as Generally Recognized as Safe (GRAS) by the United States' Food and Drug Administration (FDA).
GRAS substances according to the FDA Common nameBotanical name of plant sourceAlfalfaMedicago sativa L.AllspicePimenta officinalis Lindl.Bitter almond, free from cyanidePrunus amygdalus Batsch, Prunus armeniaca L., or Prunus persica (L.) Batsch.Ambrette (seed)Hibiscus moschatus Moench.Angelica rootAngelica archangelica L.Angelica seedAngelica stemAngostura (cusparia bark)Galipea officinalis Hancock, Angostura trifoliataAnisePimpinella anisum L.AsafetidaFerula assa-foetida L. and related spp. of FerulaBalm (lemon balm)Melissa officinalis L.Balsam of PeruMyroxylon pereirae Klotzsch.BasilOcimum basilicum L.Bay leavesLaurus nobilis L.Bay (myrcia oil)Pimenta racemosa (Mill.) J. W. Moore.Bergamot (bergamot orange)Citrus aurantium L. subsp. bergamia Wright et Arn.Bitter almond (free from prussic acid)Prunus amygdalus Batsch, Prunus armeniaca L., or Prunus persica (L.) Batsch.Bois de roseAniba rosaeodora Ducke.CacaoTheobroma cacao L.Camomile (chamomile) flowers, German or HungarianMatricaria chamomilla L.Camomile (chamomile) flowers, Roman or EnglishAnthemis nobilis L.CanangaCananga odorata Hook. f. and Thoms.CapsicumCapsicum frutescens L. and Capsicum annuum L.CarawayCarum carvi L.Cardamom seed (cardamon)Elettaria cardamomum Maton.Carob beanCeratonia siliqua L.CarrotDaucus carota L.Cascarilla barkCroton eluteria Benn.Cassia bark, ChineseCinnamomum cassia Blume.Cassia bark, Padang or BataviaCinnamomum burmanni Blume.Cassia bark, SaigonCinnamomum loureirii Nees.Celery seedApium graveolens L.Cherry, wild, barkPrunus serotina Ehrh.ChervilAnthriscus cerefolium (L.) Hoffm.ChicoryCichorium intybus L.Cinnamon bark, CeylonCinnamomum zeylanicum Nees.Cinnamon bark, ChineseCinnamomum cassia Blume.Cinnamon bark, SaigonCinnamomum loureirii Nees.Cinnamon leaf, CeylonCinnamomum zeylanicum Nees.Cinnamon leaf, ChineseCinnamomum cassia Blume.Cinnamon leaf, SaigonCinnamomum loureirii Nees.CitronellaCymbopogon nardus Rendle.Citrus peelsCitrus spp.Clary (clary sage)Salvia sclarea L.CloverTrifolium spp.Coca (decocainized)Erythroxylum coca Lam. and other spp. of ErythroxylumCoffeeCoffea spp.Cola nutCola acuminata Schott and Endl., and other spp. of ColaCorianderCoriandrum sativum L.Cumin (cummin)Cuminum cyminum L.Curaçao orange peel (orange, bitter peel)Citrus aurantium L.Cusparia barkGalipea officinalis HancockDandelionTaraxacum officinale Weber and Taraxacum laevigatum DC.Dandelion rootDog grass (quackgrass, triticum)Agropyron repens (L.) Beauv.Elder flowersSambucus canadensis L. and Sambucus nigra I.Estragole (esdragol, esdragon, tarragon)Artemisia dracunculus L.Estragon (tarragon)Fennel, sweetFoeniculum vulgare Mill.FenugreekTrigonella foenum-graecum L.Galanga (galangal)Alpinia officinarum Hance.GeraniumPelargonium spp.Geranium, East IndianCymbopogon martini Stapf.Geranium, rosePelargonium graveolens L'Her.GingerZingiber officinale Rosc.GrapefruitCitrus paradisi Macf.GuavaPsidium spp.Hickory barkCarya spp.Horehound (hoarhound)Marrubium vulgare L.HopsHumulus lupulus L.HorsemintMonarda punctata L.HyssopHyssopus officinalis L.ImmortelleHelichrysum augustifolium DC.JasmineJasminum officinale L. and other spp. of JasminumJuniper (berries)Juniperus communis L.Kola nutCola acuminata Schott and Endl., and other spp. of ColaLaurel berriesLaurus nobilis L.Laurel leavesLaurus spp.LavenderLavandula officinalis ChaixLavender, spikeLavandula latifolia Vill.LavandinHybrids between Lavandula officinalis Chaix and Lavandula latifolin Vill.LemonCitrus limon (L.) Burm. f.Lemon balm (see balm)Melissa officinalis L.LemongrassCymbopogon citratus DC. and Cymbopogon lexuosus Stapf.Lemon peelCitrus limon (L.) Burm. f.LimeCitrus aurantifolia Swingle.Linden flowersTilia spp.Locust beanCeratonia siliqua L,LupulinHumulus lupulus L.MaceMyristica fragrans Houtt.MandarinCitrus reticulata Blanco.Marjoram, sweetMajorana hortensis Moench.Mate, yerbaIlex paraguariensis St. Hil.Melissa (see balm)MentholMentha spp.Menthyl acetateMolasses (extract)Saccharum officinarum L.MustardBrassica spp.NaringinCitrus paradisi Macf.Neroli, bigaradeCitrus aurantium L.NutmegMyristica fragrans Houtt.OnionAllium cepa L.Orange, bitter, flowersCitrus aurantium L.Orange, bitter, peelOrange leafCitrus sinensis (L.) Osbeck.Orange, sweetOrange, sweet, flowersOrange, sweet, peelOriganumOriganum spp.PalmarosaCymbopogon martini Stapf.PaprikaCapsicum annuum L.ParsleyPetroselinum crispum (Mill.) Mansf.Pepper, blackPiper nigrum L.Pepper, whitePeppermintMentha piperita L.Peruvian balsamMyroxylon pereirae Klotzsch.PetitgrainCitrus aurantium L.Petitgrain lemonCitrus limon (L.) Burm. f.Petitgrain mandarin or tangerineCitrus reticulata Blanco.PimentaPimenta officinalis Lindl.Pimenta leafPipsissewa leavesChimaphila umbellata Nutt.PomegranatePunica granatum L.Prickly ash barkXanthoxylum (or Zanthoxylum) americanum Mill. or Xanthoxylum clava-herculis L.Rose absoluteRosa alba L., Rosa centifolia L., Rosa damascena Mill., Rosa gallica L., and vars. of these spp.Rose (otto of roses, attar of roses)Rose budsRose flowersRose fruit (hips)Rose geraniumPelargonium graveolens L'Her.Rose leavesRosa spp.RosemaryRosmarinus officinalis L.SaffronCrocus sativus L.SageSalvia officinalis L.Sage, GreekSalvia triloba L.Sage, SpanishSalvia officinalis subsp. lavandulifolia (Vahl) GamsSavory, summerSatureia hortensis L.Savory, winterSatureia montana L.Schinus molleSchinus molle L.Sloe berries (blackthorn berries)Prunus spinosa L.SpearmintMentha spicata L.Spike lavenderLavandula latifolia Vill.TamarindTamarindus indica L.TangerineCitrus reticulata Blanco.TarragonArtemisia dracunculus L.TeaThea sinensis L.ThymeThymus vulgaris L. and Thymus zygis var. gracilis Boiss.Thyme, whiteThyme, wild or creepingThymus serpyllum L.Triticum (see dog grass)Elymus repensTuberosePolianthes tuberosa L.TurmericCurcuma longa L.VanillaVanilla planifolia Andr. or Vanilla tahitensis J. W. Moore.Violet flowersViola odorata L.Violet leavesViolet leaves absoluteWild cherry barkPrunus serotina Ehrh.Ylang-ylangCananga odorata Hook. f. and Thoms.Zedoary barkCurcuma zedoaria Rosc.
As antimicrobials The most commonly used essential oils with antimicrobial action are: phenol-rich EOs such as Thymus spp. Origanum spp., Satureja spp., phenylpropene-rich EOs such as Cinnamomum verum cortex and leaves, Syzygium aromaticum, and alcohol-rich EOs such as Melaleuca alternifolia, Lavandula x intermedia, Lavandula angustifolia, Pelargonium spp., etc.: important antimicrobial compounds are eugenol, eugenol acetate, carvacrol, linalool, thymol, geraniol, cinnamaldehyde, geranial, neral, 1,8-cineole, methyl chavicol, methyl cinnamate, methyl eugenol, camphor, α-thujone, (Z)-linalool oxide.
Some essential oils are effective antimicrobials and have been evaluated for food incorporation in vitro. 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 and foods in chemistry (especially lipid content), viscosity, and duration of inoculation/storage.
As aromatherapy