essential oil essential oil an essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. 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. an essential oil is essential in the sense that it contains the essence of the plant's fragrance—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 or essential fatty acid, which are so called because they are nutritionally required by a living organism. not to be confused with essential fatty acid. plant oilssandalwood oil types vegetable oil (list) macerated oil (list) essential oil (list) uses drying oil oil paint cooking oil fuel biodiesel components saturated fat monounsaturated fat polyunsaturated fat trans fat essential oils are generally extracted by distillation, often by using steam. other processes include expression, solvent extraction, sfumatura, absolute oil extraction, resin tapping, wax embedding, and cold pressing. they are used in perfumes, cosmetics, soaps, air fresheners and other products, for flavoring food and drink, and for adding scents to incense and household cleaning products. essential oils are often used for aromatherapy, a form of alternative medicine 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, peppermint, tea tree oil, patchouli, and eucalyptus are distilled. raw plant material, consisting of the flowers, leaves, wood, bark, roots, seeds, or peel, is put into an alembic (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) which is purified through a fractional distillation. the recondensed water is referred to as a hydrosol, hydrolat, herbal distillate, or plant water essence, which may be sold as another fragrant product. hydrosols include rose water, lavender water, lemon balm, clary sage, and orange blossom water. expression most citrus peel oils are expressed mechanically or cold-pressed (similar to olive oil extraction). 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 byproducts 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 such as hexane or supercritical carbon dioxide is used to extract the oils. extracts from hexane and other hydrophobic solvents are called concretes, which are a mixture of essential oil, waxes, resins, and other lipophilic (oil-soluble) plant material. although highly fragrant, concretes contain large quantities of non-fragrant waxes and resins. often, another solvent, such as ethyl alcohol, is used to extract the fragrant oil from the concrete. the alcohol solution is chilled to −18 °c (0 °f) for more than 48 hours which causes the waxes and lipids 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 absolute. supercritical carbon dioxide is used as a solvent in supercritical fluid extraction. this method can avoid petrochemical 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. oiltonnes sweet orange12,000 mentha arvensis4,800 peppermint3,200 cedarwood2,600 lemon2,300 eucalyptus globulus2,070 litsea cubeba2,000 clove (leaf)2,000 spearmint1,300 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 counterirritants and, thereby, exert an antitussive (cough suppressing) effect. many essential oils, particularly tea tree oil, may cause contact dermatitis. 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. use in aromatherapy essential oils are used in aromatherapy as part of, for example, essential oil diffusers. aromatherapy is a form of alternative medicine 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. 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, 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. as of 2012 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. 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 (fda). gras substances according to the fda common name botanical name of plant source alfalfa medicago sativa l. allspice pimenta officinalis lindl. bitter almond, free from cyanide prunus amygdalus batsch, prunus armeniaca l., or prunus persica (l.) batsch. ambrette (seed) hibiscus moschatus moench. angelica root angelica archangelica l. angelica seed angelica stem angostura (cusparia bark) galipea officinalis hancock, angostura trifoliata anise pimpinella anisum l. asafetida ferula assa-foetida l. and related spp. of ferula balm (lemon balm) melissa officinalis l. balsam of peru myroxylon pereirae klotzsch. basil ocimum basilicum l. bay leaves laurus 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 rose aniba rosaeodora ducke. cacao theobroma cacao l. camomile (chamomile) flowers, german or hungarian matricaria chamomilla l. camomile (chamomile) flowers, roman or english anthemis nobilis l. cananga cananga odorata hook. f. and thoms. capsicum capsicum frutescens l. and capsicum annuum l. caraway carum carvi l. cardamom seed (cardamon) elettaria cardamomum maton. carob bean ceratonia siliqua l. carrot daucus carota l. cascarilla bark croton eluteria benn. cassia bark, chinese cinnamomum cassia blume. cassia bark, padang or batavia cinnamomum burmanni blume. cassia bark, saigon cinnamomum loureirii nees. celery seed apium graveolens l. cherry, wild, bark prunus serotina ehrh. chervil anthriscus cerefolium (l.) hoffm. chicory cichorium intybus l. cinnamon bark, ceylon cinnamomum zeylanicum nees. cinnamon bark, chinese cinnamomum cassia blume. cinnamon bark, saigon cinnamomum loureirii nees. cinnamon leaf, ceylon cinnamomum zeylanicum nees. cinnamon leaf, chinese cinnamomum cassia blume. cinnamon leaf, saigon cinnamomum loureirii nees. citronella cymbopogon nardus rendle. citrus peels citrus spp. clary (clary sage) salvia sclarea l. clover trifolium spp. coca (decocainized) erythroxylum coca lam. and other spp. of erythroxylum coffee coffea spp. cola nut cola acuminata schott and endl., and other spp. of cola coriander coriandrum sativum l. cumin (cummin) cuminum cyminum l. curaçao orange peel (orange, bitter peel) citrus aurantium l. cusparia bark galipea officinalis hancock dandelion taraxacum officinale weber and taraxacum laevigatum dc. dandelion root dog grass (quackgrass, triticum) agropyron repens (l.) beauv. elder flowers sambucus canadensis l. and sambucus nigra i. estragole (esdragol, esdragon, tarragon) artemisia dracunculus l. estragon (tarragon) fennel, sweet foeniculum vulgare mill. fenugreek trigonella foenum-graecum l. galanga (galangal) alpinia officinarum hance. geranium pelargonium spp. geranium, east indian cymbopogon martini stapf. geranium, rose pelargonium graveolens l'her. ginger zingiber officinale rosc. grapefruit citrus paradisi macf. guava psidium spp. hickory bark carya spp. horehound (hoarhound) marrubium vulgare l. hops humulus lupulus l. horsemint monarda punctata l. hyssop hyssopus officinalis l. immortelle helichrysum augustifolium dc. jasmine jasminum officinale l. and other spp. of jasminum juniper (berries) juniperus communis l. kola nut cola acuminata schott and endl., and other spp. of cola laurel berries laurus nobilis l. laurel leaves laurus spp. lavender lavandula officinalis chaix lavender, spike lavandula latifolia vill. lavandin hybrids between lavandula officinalis chaix and lavandula latifolin vill. lemon citrus limon (l.) burm. f. lemon balm (see balm) melissa officinalis l. lemongrass cymbopogon citratus dc. and cymbopogon lexuosus stapf. lemon peel citrus limon (l.) burm. f. lime citrus aurantifolia swingle. linden flowers tilia spp. locust bean ceratonia siliqua l, lupulin humulus lupulus l. mace myristica fragrans houtt. mandarin citrus reticulata blanco. marjoram, sweet majorana hortensis moench. mate, yerba ilex paraguariensis st. hil. melissa (see balm) menthol mentha spp. menthyl acetate molasses (extract) saccharum officinarum l. mustard brassica spp. naringin citrus paradisi macf. neroli,