Essential oil

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.

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

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. As of 2012^[update] 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

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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

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

Essential oils are used in aromatherapy for relaxation, particularly by people having nausea and pain caused by cancer and chemotherapy. Using essential oils for aromatherapy may give symptom relief from end of life conditions, anxiety, depression, stress or insomnia, and for hospital or home settings in critical care or palliative care.

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. There are, however, hundreds of species of eucalyptus, and perhaps some dozens are used to various extents as sources of essential oils.

Lavender oil

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.

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.

Handling

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.

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. 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.

Essential oils can be toxic if ingested or absorbed through the skin.

Pregnancy

Some essential oils should not be used by pregnant or breastfeeding women, because they can be abortifacients, cause fetal damage, or disrupt hormones. 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.

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.

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.