Essential oils are composed of hydrophobic volatile organic compounds, usually in liquid form, obtained from plant material. 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 the oil contains the fragrance or essence of the 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.
Essential oils, according to ISO, are produced either by steam distillation, by mechanical manipulation of the rind of the fruits of the genus Citrus (also called cold pressing), or by dry distillation. Other methods, such as solvent extraction, are not accepted and, in fact, result in different perfumed products (pommades, concretes, and absolutes). They are used in perfumes, cosmetics, soaps, air fresheners and other products, for flavoring food and drink, and for adding scents to household cleaning products.
Essential oils are often used for aromatherapy. 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 toxic if ingested or absorbed through the skin. 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.
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.
:{| 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 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 (mainly eucalyptus) have been increasingly causing cases of poisoning, mostly of children. During the years 2014 to 2018, there were 4,412 poisoning incidents reported in New South Wales.
Use in aromatherapy
thumb|Essential oils can be used in aromatherapy by using essential oil diffusers
An overview of systematic reviews found that while aromatherapy has been studied for conditions like anxiety, depression, and pain, the evidence is generally of poor quality and not convincing enough to support its effectiveness. Use of essential oils may cause harm including allergic reactions and skin irritation. There has been at least one case of death. and anxiety.
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, 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.
GRAS substances according to the FDA
|Prunus amygdalus Batsch, Prunus armeniaca L., or Prunus persica (L.) Batsch.
|-
|Ambrette (seed)
|Hibiscus moschatus Moench.
|-
|Angelica root
|rowspan=3|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
|rowspan=2|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)
|rowspan=2|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
|rowspan=2|Mentha spp.
|-
|Menthyl acetate
|-
|Molasses (extract)
|Saccharum officinarum L.
|-
|Mustard
|Brassica spp.
|-
|Naringin
|Citrus paradisi Macf.
|-
|Neroli, bigarade
|Citrus aurantium L.
|-
|Nutmeg
|Myristica fragrans Houtt.
|-
|Onion
|Allium cepa L.
|-
|Orange, bitter, flowers
|rowspan=2|Citrus aurantium L.
|-
|Orange, bitter, peel
|-
|Orange leaf
|rowspan=4|Citrus sinensis (L.) Osbeck.
|-
|Orange, sweet
|-
|Orange, sweet, flowers
|-
|Orange, sweet, peel
|-
|Origanum
|Origanum spp.
|-
|Palmarosa
|Cymbopogon martini Stapf.
|-
|Paprika
|Capsicum annuum L.
|-
|Parsley
|Petroselinum crispum (Mill.) Mansf.
|-
|Pepper, black
|rowspan=2|Piper nigrum L.
|-
|Pepper, white
|-
|Peppermint
|Mentha piperita L.
|-
|Peruvian balsam
|Myroxylon pereirae Klotzsch.
|-
|Petitgrain
|Citrus aurantium L.
|-
|Petitgrain lemon
|Citrus limon (L.) Burm. f.
|-
|Petitgrain mandarin or tangerine
|Citrus reticulata Blanco.
|-
|Pimenta
|rowspan=2|Pimenta officinalis Lindl.
|-
|Pimenta leaf
|-
|Pipsissewa leaves
|Chimaphila umbellata Nutt.
|-
|Pomegranate
|Punica granatum L.
|-
|Prickly ash bark
|Xanthoxylum (or Zanthoxylum) americanum Mill. or Xanthoxylum clava-herculis L.
|-
|Rose absolute
|rowspan=5|Rosa alba L., Rosa centifolia L., Rosa damascena Mill., Rosa gallica L., and vars. of these spp.
|-
|Rose (otto of roses, attar of roses)
|-
|Rose buds
|-
|Rose flowers
|-
|Rose fruit (hips)
|-
|Rose geranium
|Pelargonium graveolens L'Her.
|-
|Rose leaves
|Rosa spp.
|-
|Rosemary
|Rosmarinus officinalis L.
|-
|Saffron
|Crocus sativus L.
|-
|Sage
|Salvia officinalis L.
|-
|Sage, Greek
|Salvia triloba L.
|-
|Sage, Spanish
|Salvia officinalis subsp. lavandulifolia (Vahl) Gams
|-
|Carob
|Ceratonia siliqua L.
|-
|Savory, summer
|Satureia hortensis L.
|-
|Savory, winter
|Satureia montana L.
|-
|Schinus molle
|Schinus molle L.
|-
|Sloe berries (blackthorn berries)
|Prunus spinosa L.
|-
|Spearmint
|Mentha spicata L.
|-
|Spike lavender
|Lavandula latifolia Vill.
|-
|Tamarind
|Tamarindus indica L.
|-
|Tangerine
|Citrus reticulata Blanco.
|-
|Tarragon
|Artemisia dracunculus L.
|-
|Tea
|Thea sinensis L.
|-
|Thyme
|rowspan=2|Thymus vulgaris L. and Thymus zygis var. gracilis Boiss.
|-
|Thyme, white
|-
|Thyme, wild or creeping
|Thymus serpyllum L.
|-
|Triticum (see dog grass)
|Elymus repens
|-
|Tuberose
|Polianthes tuberosa L.
|-
|Turmeric
|Curcuma longa L.
|-
|Vanilla
|Vanilla planifolia Andr. or Vanilla tahitensis J. W. Moore.
|-
|Violet flowers
|rowspan=3|Viola odorata L.
|-
|Violet leaves
|-
|Violet leaves absolute
|-
|Wild cherry bark
|Prunus serotina Ehrh.
|-
|Ylang-ylang
|Cananga odorata Hook. f. and Thoms.
|-
|Zedoary bark
|Curcuma 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.
Dilution
Essential oils are usually lipophilic (literally: "oil-loving") compounds that are immiscible (not miscible) with water. They can be diluted in solvents like pure ethanol and polyethylene glycol.
==Raw materials==<!-- This section is linked from Vegetable fats and oils -->
Essential oils are derived from sections of plants. Some plants, like the bitter orange, are sources of several types of essential oil.
:{| class="wikitable" |
| valign="top" |
;Bark
- Cassia
- Cinnamon
- Sassafras
;Berries
- Allspice
- Juniper
;Flowers
- Cannabis
- Chamomile
- Clary sage
- Clove
- Hops
- Hyssop
- Jasmine
- Lavender
- Manuka
- Marjoram
- Orange
- Pelargonium (Scented geranium)
- Plumeria
- Rose
- Ylang-ylang
| valign="top" |
;Leaves
- Basil
- Bay leaf
- Buchu
- Cinnamon
- Common sage
- Eucalyptus
- Guava
- Lemon grass
- Melaleuca
- Oregano
- rose
- bergamot
- Patchouli
- Peppermint
- Pine
- Rosemary
- Spearmint
- Tea tree
- Thyme
- Tsuga
- Wintergreen
;Peel
- Bergamot
- Grapefruit
- Lemon
- Lime
- Orange
- Tangerine
| valign="top" |
;Resin
<!-- not sure if fossilized tree resins count * Amber --><!-- not sure if a balsam would count or not * Balsam Tolu -->
- Benzoin
- Copaiba
- Frankincense
- Labdanum
- Myrrh
;Rhizome
- Galangal
- Ginger
;Roots
- Valerian
;Seeds
- Anise
- Buchu
- Celery
- Cumin
- Flax
- Nutmeg oil
;Woods
- Agarwood
- Camphor
- Cedar
- Rosewood
- Sandalwood
|}
Balsam of Peru
Balsam of Peru, an essential oil derived from Myroxylon 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 clinics.
Garlic oil
Garlic oil is an essential oil derived from garlic.
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
thumb|Lavender essential oil sold at a market in [[France]]
Lavender oil has long been used in the production of perfume. 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
There are two major species of rose whose petals used for the production of Rose oil; Rosa damascena and Rosa centifolia.
Rose oils can be classified according to their botanical name, their place of origin and their extraction process.
Steam-distilled rose oil is known as "rose otto", while the solvent extracted oil is known as "rose absolute".
Rose otto is extracted through hydro-distillation, in which Rosa damascena petals are slowly heated with water. The heat causes the petals to release the essential rose oil. When cooled, the oil (rose otto) floats to the surface of the water (rose hydrosol). In contrast, rose absolute is solvent-extracted. Rose petals are combined with an organic solvent in a slowly rotating drum to draw out the aromatic matter from the flowers. After the solvent is evaporated, the waxy substance remaining is called rose concrete. Rose concrete is filtered with ethanol alcohol to remove waxes and non-aromatic components and leave behind the liquid known as rose absolute.
Toxicity
<!-- please consider updating the aromatherapy article's section on safety/danger when you update this. -->
The potential toxicity of essential oil is related to the toxicity of specific chemical components of the oil, and to its level or grade of purity. This might cause them to be more susceptible to toxic effects than adults.
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 Class 3 Flammable Liquids, as they have a flash points at or below 60 °C.
Gynecomastia
Estrogenic and antiandrogenic activity have been reported by in vitro study of tea tree oil and lavender essential oils. Two published sets of case reports suggest that lavender oil may be implicated in some cases of gynecomastia, 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 BBC report on a study stated that tea tree and lavender oils contain eight substances that when tested in tissue culture experiments, increasing the level of estrogen and decreasing the level of testosterone. Some of the substances are found in "at least 65 other essential oils". The study did not include animal or human testing.
Handling
Exposure to essential oils may cause contact dermatitis. Pharmacopoeia standards for medicinal oils should be heeded.
The internal use of essential oils can pose hazards to pregnant women, as some can be abortifacients or cause fetal damage, and thus should not be used during pregnancy.
Some oils can be toxic to some domestic animals, cats in particular.
Pesticide residues
Concern about pesticide residues in essential oils, particularly those used therapeutically, means many practitioners of aromatherapy buy organically produced oils. Not only are pesticides present in trace quantities, but also the oils themselves are used in tiny quantities and usually in high dilutions. Where there is a concern about pesticide residues in food essential oils, such as mint or orange oils, the proper criterion is not solely whether the material is organically produced, but whether it meets the government standards based on actual analysis of its pesticide content.
Pregnancy
Some essential oils should not be used by pregnant or breastfeeding women, because they can be abortifacients, cause fetal damage, or disrupt hormones.
Some essential oils may contain impurities or additives that may be harmful. Some uses of essential oils may be safe during pregnancy (e.g. smelling lavender to reduce stress), but care must be taken when selecting quality and brand.
Sensitivity to certain smells may cause pregnant women to have adverse side effects with essential oil use, such as headache, vertigo, and nausea. Pregnant women often report a heightened sensitivity to smells and taste, and essential oils can cause irritation and nausea if ingested.
{| class="wikitable"
|-
! Common name !! Oral LD<sub>50</sub>!! Dermal LD<sub>50</sub> !! Notes
|-
| Neem || 14 mg/kg|| >2 mg/kg ||
|-
| Lemon myrtle || 2.43 mg/kg || 2.25 mg/kg ||
|-
| Frankincense || >5 mg/kg || >5 mg/kg || Boswellia carterii
|-
| Frankincense || >2 mg/kg || >2 mg/kg || Boswellia sacra
|-
| Indian frankincense || >2 mg/kg || >2 mg/kg || Boswellia serrata
|-
| Ylang-ylang || >5 mg/kg || >5 mg/kg ||
|-
| Cedarwood || >5 mg/kg || >5 mg/kg ||
|-
| Roman chamomile || >5 mg/kg || >5 mg/kg ||
|-
| White camphor || >5 mg/kg || >5 mg/kg || Cinnamomum camphora, extracted from leaves
|-
| Yellow camphor || 3.73 mg/kg || >5 mg/kg || Cinnamomum camphora, extracted from bark
|-
| Hot oil || 3.80 mg/kg || >5 mg/kg || Cinnamomum camphora, oil extracted from leaves
|-
| Cassia || 2.80 mg/kg || 0.32 mg/kg ||
|}
Standardization of derived products
In 2002, ISO published ISO 4720 in which the botanical names of the relevant plants are standardized. The rest of the standards with regards to this topic can be found in the section of ICS 71.100.60.
History
The resins of aromatics and plant extracts were retained to produce traditional medicines and scented preparations, such as perfumes and incense, including frankincense, myrrh, cedarwood, juniper berry and cinnamon.
Essential oils have been used in folk medicine over centuries. The Persian physician Ibn Sina, known as Avicenna in Europe, was first to derive the fragrance of flowers from distillation, while the earliest recorded mention of the techniques and methods used to produce essential oils may be Ibn al-Baitar (1188–1248), an Arab Al-Andalusian (Muslim Spain) physician, pharmacist and chemist.
Rather than refer to essential oils themselves, modern works typically discuss specific chemical compounds of which the essential oils are composed, such as referring to methyl salicylate rather than "oil of wintergreen".
See also
- Aroma lamp
- Enfleurage
- Fragrance oil
- List of essential oils
- Tincture
- Volatility