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KETONES

Ketones are the most potentially toxic compounds in essential oils. The effect they produce upon the body's systems are extremely powerful and too much ketone is what makes oils too dangerous to use in Aromatherapy.

They can cause spontaneous abortions, provoke an epileptic fit, or poison the central nervous system.

However, in very small amounts they can be of very valuable use in Aromatherapy. They stimulate the immune system, are anti-fungal etc, BUT safer alternatives usually can be found. Use of these oils should be by a professional Aromatherapist only.

Some oils that contain ketones are Mugwort, Sage, Thuja, they contain the most dangerous ketone of them all called Thujone.

Another ketone called borneone is found in Camphor, Cinnamon, Mugwort, Spike Lavender.

Carvone (another ketone) is found in caraway, peppermint and many other oils.

In pennyroyal there is pulegone,  Hyssop has pinocamphone, 

Any ketone (you can tell it's a ketone by the last three letters "one") that is listed high as an active constituent in your essential oils, is ALWAYS to be mixed with a carrier oil and used with caution

Oils that contain medium amounts of Ketonse are as follows:

Roman chamomile, medium amounts of pinocarvone

Hyssop, medium amounts of pinocamphone

Lavandin, medium amounts of camphor

Peppermint, medium amounts of menthone

Sage, medium amounts of thujone

MONOTERPENES(subsection of Terpenes.

Monoterpenes are found in practically all your essential oils. Amongst the effects that they give (although not very strong) are: bactericidal, stimulating, expectorant, slightly analgesic and in the air are antiseptic. Please note that monoterpenes can be irritating to the skin and any oil containing a high amount of monoterpenes MUST be used with a carrier oil.

All citrus oils (except Bergemot) contain a high amount of a terpene called dextro-limonene and these actually quench the irritating effects of an oil that is high in aldehyde (such as bergamot or lemongrass) rendering it safe to use.

There are also dipentene, pinene,camphene and sylvestrene. Note the last three letters of the compound (ene) and you can tell it's a terpene. Remember "one" for a ketone and now ene for a terpene.

Now I'll give you a list of oils that contain a medium to large amount of terpenes:

Black Pepper Medium amounts of limonene and pinene

Moroccan Chamomile, medium amounts of pinene

Roman Chamomile, medium amounts of pinene

Eucalyptus, medium amounts of pinene

Fennel, medium amounts of limonene

Frankincense, medium amounts of limonene and pinene

Grapefruit, large amounts of limonene

Hyssop, medium amounts of pinene

Juniper, large amounts of pinene and medium amounts of sabinene

Lemon, large amounts of limonene

Sweet Marjoram, medium amounts of sabinene

Neroli, medium amounts of limonene and pinene

Nutmeg, medium amounts of pinene and sabinene

Sweet Orange, large amounts of limonene

Pine, medium amounts of limonene and large amounts of pinene

Rosemary, medium amounts of pinene

ALDEHYDES

Aldehydes fall in properties somewhere between Alcohols and Ketones. A few aldehydes tend to be skin sensitizes and cause a skin reaction such as a rash when two like Aldehydes meet in a mixture.

Aldehydes are anti-inflammatory, anti-infectious, tonic, hypotensive, calming to the nervous system and temperature reducing. Please note it is important to store oils with Aldehydes properly as an poorly kept oil or one kept for too long can form unwanted acids, making the oil useless for theraputic purposes.

Please note you can tell an aldehyde by the ending "al" or it will contain the word aldehyde in it's name : ex, cinnamic Aldehyde.

Oils containing large or medium amounts of Aldehydes are:

Bergamot, large amounts of citral

Lemon grass, large amounts of citral

Melissa (true), medium amounts of citral and geranial

ALCOHOLS

Alcohols are the one compound most desired when using oils for children and the elderly (and my first choice when I was working with show dogs). They are strong bactericides, antiviral, anti-infectious, warming, stimulating, good general tonics and seem to be free of any hazards including skin irritations.

You can recognize alcohols by the ending "ol" but be careful as Phenols which can be highly irritating to mucus membranes and the skin.

Those with high or low alcohols are:

basil, large amounts of linalool

bergamot, large amounts of linalool

Clary sage, medium amounts of linalool

Geranium, with medium amounts of citronellol and geraniol

Lavendin, with medium amounts of linalol

Lavender, with large amounts of Linalol

Spanish Marjoram, with medium amounts of linalol

Sweet Marjoram with medium amounts of alpha-terpineol and terpinen-4-ol

Neroli with medium amounts of linalol

nutmeg with medium amounts of alpha-terpineol

peppermint with large amounts of menthol (big surprise that one eh?)

pettigrain with medium amounts of linalol

rose otto with medium amounts of citronellol, geraniol, and nerol

Rosemary with medium amounts of cedrol

Tea-tree with large amounts of terpinen-4-ol

Sweet thyme (not to be confused with red thyme which has large amounts of phenols) has large amounts of geraniol or linalol or medium amounts of thujanol-4. Sweet thyme will not contain ALL these, it's an either or situation.

Ylang-Ylang with large amounts of linalol

ESTERS

Esters are very gentle in the way they work and are free from hazards except for Wintergreen and birch oils which we don't use in Aromatherapy anyway, both are almost always fake oils anyway. Esters are effective on skin rashes and inflammations as they are anti-inflammatory and they are also very balancing to the nervous system. In other words they are both calming and uplifting.

Oh! recognize esters with the last three letters of "ate"

Oils with medium or large amount of esters are:

Bergamot, with medium amounts of linalyl acetate

Clary sage, with large amounts of linalyl acetate

Lavendin, with medium amounts of linalyl acetate

Lavender with medium amounts of linalyl acetate

Lemon Grass with medium amounts of geranyl acetate and linaly acetate

Neroli with large amounts of linaly acetate

Pettigrain with large amounts of linaly acetate

Note: Shirley Price also mentions that Roman Chamomile is about 80% esters rose otto is about 5% esters, Patchouli is about 18% and Sweet European Basil is about 8%.