An essential oil is a concentrated, hydrophobic liquid containing volatile aroma
compounds from plants. They are also known as volatile or ethereal oils, or simply as
the "oil of" the plant material from which they were extracted, such as oil of clove. An oil
is "essential" in the sense that it carries a distinctive scent, or essence, of the plant.
Essential oils do not as a group need to have any specific chemical properties in common,
beyond conveying characteristic fragrances. They are not to be confused with essential
fatty acids.
Essential oils are generally extracted by distillation. Other processes include expression,
or solvent extraction. They are used in perfumes, cosmetics and bath products, for
flavoring food and drink, and for scenting incense and household cleaning products.
Various essential oils have been used medicinally at different periods in history. Medical
applications proposed by those who sell medicinal oils range from skin treatments to
remedies for cancer, and are often based on historical use of these oils for these purposes.
Such claims are now subject to regulation in most countries, and have grown
correspondingly more vague, to stay within these regulations.
Interest in essential oils has revived in recent decades, with the popularity of
aromatherapy, a branch of alternative medicine which claims that the specific aromas
carried by essential oils have curative effects. Oils are volatilized or diluted in a carrier
oil and used in massage, or burned as incense, for example.
Contents
[hide]

1 Production
o
1.1 Distillation
o
1.2 Expression
o
1.3 Solvent extraction
o
1.4 Production quantities

2 Essential oil use in aromatherapy

3 Dilution

4 Raw Materials
o

4.1 Rose oil
5 Dangers
o
5.1 Gynecomastia
o
5.2 Pesticide residues

o
5.3 Ingestion
o
5.4 Smoke
o
5.5 Flammable Liquid
o
5.6 Toxicology
6 Notes and references
o

6.1 Additional references
7 See also
[edit] Production
Main article: Extraction (fragrance)
[edit] Distillation
See also: distillation
Today, most common essential oils, such as lavender, peppermint, 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 takes 22 hours to complete 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. Popular hydrosols are rose
water, lavender water, lemon balm, clary sage and orange blossom water. The use of
herbal distillates in cosmetics is increasing. Some plant hydrosols have unpleasant smells
and are therefore not sold.
[edit] Expression
Most citrus peel oils are expressed mechanically, or cold-pressed. Due to the large
quantities of oil in citrus peel and the relatively low cost to grow and harvest the raw
materials, citrus-fruit oils are cheaper than most other essential oils. Lemon or sweet
orange oils that are obtained as by-products of the citrus industry are even cheaper.
Prior to the discovery of distillation, all essential oils were extracted by pressing.
[edit] Solvent extraction
Most flowers contain too little volatile oil to undergo expression and 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 solvent are called concretes,
which is 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. As such another solvent, often ethyl alcohol, which only dissolves the fragrant
low-molecular weight compounds, is used to extract the fragrant oil from the concrete.
The alcohol is removed by a second distillation, leaving behind the absolute.
Supercritical carbon dioxide is used as a solvent in supercritical fluid extraction. This
method has many benefits, including avoiding petrochemical residues in the product. 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 and provides for a
superior product. When the extraction is complete, the pressure is reduced to ambient and
the carbon dioxide reverts back to a gas, leaving no residue. Although supercritical
carbon dioxide is also used for making decaffeinated coffee, the actual process is
different.
[edit] 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.[1]
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
[edit] Essential oil use in aromatherapy
Main article: 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. Many common
essential oils have medicinal properties that have been applied in folk medicine since
ancient times and are still widely used today. For example, many essential oils have
antiseptic properties.[2] Many are also claimed to have an uplifting effect on the mind.
The claims are supported in some studies[3][4] and unconfirmed in others.[5]
[edit] Dilution
Essential oils are usually lipophilic (literally: "oil-loving") compounds that usually are
not miscible with water. Instead, they can be diluted in solvents like pure ethanol
(alcohol), polyethylene glycol, or oils.
[edit] Raw Materials
Main article: List of essential oils
Essential oils are derived from various sections of plants. Some plants, like the bitter
orange, are sources of several types of essential oil.
Berries
Leaves
Flowers

Allspice

Basil

Cannabis

Juniper

Bay leaf

Chamomile

Cinnamon

Clary sage
Seeds

Almond

Common sage

Clove

Anise

Eucalyptus

Geranium

Celery

Lemon grass

Hops

Cumin

Melaleuca

Hyssop

Nutmeg oil

Oregano

Jasmine

Patchouli

Lavender
Bark

Cassia

Peppermint

Manuka

Cinnamon

Pine

Marjoram

Sassafras

Rosemary

Orange

Spearmint

Rose

Tea tree

Ylang-ylang

Thyme

Wintergreen
Wood

Camphor

Cedar

Rosewood

Sandalwood Resin

Agarwood
Rhizome
Peel

Bergamot

Grapefruit

Frankincense

Lemon

Myrrh

Lime

Galangal

Orange

Ginger

Tangerine
Root

Valerian
[edit] Rose oil
Main article: Rose oil
The most well-known essential oil is probably rose oil, 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".
[edit] Dangers
Because of their concentrated nature, essential oils generally should not be applied
directly to the skin in their undiluted or "neat" form. Some can cause severe irritation, or
provoke an allergic reaction. Instead, essential oils should be blended with a vegetablebased "carrier" oil (a.k.a., a base, or "fixed" oil) before being applied. Common carrier
oils include olive, almond, hazelnut and grapeseed. Common ratio of essential oil
disbursed in a carrier oil is 0.5–3% (most under 10%), and depends on its intended
purpose. Some essential oils, including many of the citrus peel oils, are photosensitizers
(i.e., increasing the skin's vulnerability to sunlight, making it more likely to burn).
Lavender oil, though generally considered the mildest essential oil, is cytotoxic to human
skin cells[6].
Industrial users of essential oils should consult the material safety data sheets (MSDS) to
determine the hazards and handling requirements of particular oils.
[edit] Gynecomastia
Estrogenic and antiandrogenic activity have been reported by in vitro study of tea tree oil
and lavender essential oils. Case reports suggest that the oils may be implicated in some
cases of gynecomastia, an abnormal breast tissue growth, in prepubescent boys.[7][8]
[edit] Pesticide residues
There is some concern about pesticide residues in essential oils, particularly those used
therapeutically. For this reason, many practitioners of aromatherapy choose to buy
organically produced oils.
[edit] Ingestion
While some advocate the ingestion of essential oils for therapeutic purposes, this should
never be done except under the supervision of a professional who is licensed to prescribe
such treatment. Some very common essential oils such as Eucalyptus are extremely toxic
internally. Pharmacopoeia standards for medicinal oils should be heeded. Essential oils
should always be kept out of the reach of children. Some oils can be toxic to some
domestic animals, cats in particular. Owners must ensure that their pets do not come into
contact with potentially harmful essential oils.[9] The internal use of essential oils should
be fully avoided during pregnancy without consulting with a licensed professional, as
some can be abortifacients in dose 0.5–10 ml.
[edit] Smoke
The smoke from burning essential oils may contain potential carcinogens, such as
polycyclic aromatic hydrocarbons (PAHs). Essential oils are naturally high in volatile
organic compounds (VOCs).
[edit] Flammable Liquid
The flash point of an essential oil is different for each oil. Many of the common essential
oils such as tea tree, lavender, and citrus oils are classed as a Class 3 Flammable Liquid
as they have a flash point of 50-60 °C. Care should be taken when shipping essential oils
to ensure the correct procedures are followed for transporting dangerous goods.
[edit] Toxicology
LD50 of most essential oils or their main components are 0.5-10 g/kg (orally or skin
test).[citation needed