Essential oil

Distillation

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) connected to a steam generator (indirect steam distillation) or over water (direct steam distillation). As the water is heated, the steam passes through the plant material, vaporizing the volatile compounds. The vapors flow through a condenser, where they condense back to liquid, which is then collected in the receiving vessel, also called a Florentine Flask.

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.

The national association for Holistic aromatherapy and medical research published by the NIH report that some essential oils can cause allergic reactions, skin irritation, hormone disruption, and even toxicity if ingested or improperly applied. Poison control centers have documented increase calls related to essential oil exposure, especially in children.

Expression

Most citrus peel oils are expressed mechanically or cold-pressed.^[7] 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.^[8]

More information Oil, Tonnes ...

Oil	Tonnes
Sweet orange	12,000
Mentha arvensis	4,800
Peppermint	3,200
Cedarwood	2,600
Lemon	2,300
Eucalyptus globulus	2,070
Litsea cubeba	2,000
Clove (leaf)	2,000
Spearmint	1,300

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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.^[28]

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.^[28]

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.^[29] 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.^[30][31][32]

Garlic oil

Garlic oil is an essential oil derived from garlic.^[33]

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.^[34] 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.^[35]

Lavender oil

Lavender oil has long been used in the production of perfume.^[36] However, studies have shown it can be estrogenic and antiandrogenic, causing problems for prepubescent boys and pregnant women, in particular.^[37] Lavender essential oil is also used as an insect repellent.^[38]

Rose oil

There are two major species of rose whose petals used for the production of Rose oil; Rosa damascena and Rosa centifolia.^[39] 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.^[40]

Flammability

The flash point of each essential oil is different. Many of the common essential oils, such as tea tree, lavender, and citrus oils,^[44][45][46] are classed as Class 3 Flammable Liquids, as they have a flash points at or below 60 °C.^[47]

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.^[48][49] 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.^[50] 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.^[51]

Handling

Exposure to essential oils may cause contact dermatitis.^[12][13][14] 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.

Ingestion

Some essential oils qualify as GRAS flavoring agents for use in foods, beverages, and confectioneries according to strict good manufacturing practice and flavorist standards.^[26] Pharmacopoeia standards for medicinal oils should be heeded.^[52]

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.^[41] Some oils can be toxic to some domestic animals, cats in particular.^[53]

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.^[54]

Pregnancy

Some essential oils should not be used by pregnant or breastfeeding women, because they can be abortifacients, cause fetal damage, or disrupt hormones.^[41] Key components of essential oils and whole essential oils do not always have the same hormonal effects. Minor compounds in whole oils may have both individual or group (synergistic) effects.^[55] Some essential oils may contain impurities or additives that may be harmful.^[56] Some uses of essential oils may be safe during pregnancy (e.g. smelling lavender to reduce stress^[57]), 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,^[58] and essential oils can cause irritation and nausea if ingested.^[6]

Toxicology

The following table lists the LD₅₀ 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.^[59]