An essential oil is a concentrated hydrophobic
liquid containing volatile
(easily evaporated at normal temperatures) chemical compound
s from plant
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
. 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 given living organism.
Essential oils are generally extracted by distillation
, often by using steam
. Other processes include expression
, solvent extraction
oil extraction, resin tapping, wax embedding, and cold pressing. They are used in perfumes
s and other products, for flavoring
food and drink, and for adding scents to incense
and household cleaning products. Essential oils should not be confused with perfume, fragrance, etc. as the latter usually include pure chemical components whereas essential oils are derived from plants.
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, and children may be particularly susceptible to the toxic effects of improper use.
Essential oils have been used in folk medicine
throughout history. The earliest recorded mention of the techniques and methods used to produce essential oils is believed to be that of Ibn al-Baitar
(1188–1248), an Al-Andalus
ian (Muslim Spain) physician
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".
Interest in essential oils has revived in recent decades with the popularity of aromatherapy
, a branch of alternative medicine
that uses essential oils and other aromatic compounds. Oils are volatilized, diluted in a carrier oil
and used in massage, diffused in the air by a nebulizer
or diffuser, heated over a candle flame, or burned as incense.
Medical applications proposed by those who sell medicinal oils range from skin treatments to remedies for cancer
and often are based solely on historical accounts of use of essential oils for these purposes. Claims for the efficacy of medical treatments, and treatment of cancers in particular, are now subject to regulation in most countries.
Most common essential oils such as lavender
, tea tree oil
, and eucalyptus
are distilled. Raw plant material, consisting of the flower
s, 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
water, lemon balm
, clary sage
, and orange blossom water
. The use of herbal distillates in cosmetics
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 byproduct
s of the citrus industry.
Before the discovery of distillation, all essential oils were extracted by pressing.
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, wax
s, 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 for more than 48 hours which causes the wax
es and lipid
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 ''absolute
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.
is another solvent used to obtain essential oils. It was originally developed as a refrigerant to replace Freon. Although Florasol is an "ozone-friendly" product, it has a high global warming potential
(GWP; 100-yr GWP = 1430). The European Union has banned its use, with a phase-out process that began in 2011, to be completed in 2017. One advantage of Florasol is that the extraction of essential oils occurs at or below room temperature so degradation through high temperature extremes does not occur. The essential oils are mostly pure and contain little to no foreign substances.
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
s and, thereby, exert an antitussive
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
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. As such, the use of essential oils as an alternative medicine should be approached with caution.
Use as pesticide
Research has shown that 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 other than pests. Essential oils that have been investigated include rose, lemon grass, lavender, thyme, peppermint, 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.
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
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. The most common way to safely dilute essential oils for topical use is in a carrier oil. This can be any vegetable oil readily available, the most popular for skin care being jojoba, coconut, wheat germ, olive and avocado.
Essential oils are derived from sections of plants. Some plants, like the bitter orange, are sources of several types of essential oil.
Balsam of Peru
Balsam of Peru, an essential oil derived from the ''Myroxylon'', is used in food and drink for flavoring, in perfumes and toiletries for fragrance, and in medicine and pharmaceutical items for healing properties. However, a number of national and international surveys have identified Balsam of Peru as being in the "top five" allergens most commonly causing patch test allergic reactions in people referred to dermatology clinics.
Garlic oil is an essential oil derived from garlic.
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 has long been used in the production of perfume. However, 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 is 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".
The potential danger of an essential oil is sometimes relative to its level or grade of purity, and sometimes related 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 or "neat" form. Some can cause severe irritation, provoke an allergic reaction and, over time, prove hepatotoxic.
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 safety data sheets 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.
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 point of 50–60 °C.
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.
Exposure to essential oils may cause contact dermatitis.
Essential oils can be aggressive toward rubbers and plastics, so care must be taken in choosing the correct handling equipment. Glass syringes are often used, but have coarse volumetric graduations. Chemistry syringes are ideal, as they resist essential oils, are long enough to enter deep vessels, and have fine graduations, facilitating quality control. Unlike traditional pipettes, which have difficulty handling viscous fluids, the chemistry syringe, also known as a positive displacement pipette, has a seal and piston arrangement which slides inside the pipette, wiping the essential oil off the pipette wall.
Some essential oils qualify as GRAS flavoring agents for use in foods, beverages, and confectioneries according to strict good manufacturing practice and flavorist standards.
[ ] Pharmacopoeia standards for medicinal oils should be heeded. Some oils can be toxic to some domestic animals, cats in particular. The internal use of essential oils can pose hazards to pregnant women, as some can be abortifacients in dose 0.5–10 mL, and thus should not be used during pregnancy.
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. 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.
Certain essential oils are safe to use during pregnancy, but care must be taken when selecting quality and brand. Some essential oils may contain impurities and additives that may be harmful to pregnant women. 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 an abnormal sensitivity to smells and taste, and essential oils can cause irritation and nausea when ingested. Always consult a doctor before use.
The following table lists the or median lethal dose for common oils; this is the dose required to kill half the members of a tested animal population. LD50 is intended as a guideline only, and reported values can vary widely due to differences in tested species and testing conditions.
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
* Aroma lamp
* Fragrance oil
* List of essential oils