Essential Oils are made up of chemical compounds, and the constituents of the oils are classified depending on the chemical groupings. Generally, Essential Oils are made up from chemical compounds containing hydrogen, oxygen and carbon, and can be divided into 2 groupings:
ALCOHOLS
Alcohols have a solvent action and are able to dissolve other substances, forming a solution. Alcohols tend to be stimulating and anti-bacterial. Essential Oils which contain a high quantity of alcohols include Lavender, Tea Tree, Geranium, Neroli but are considered as low toxicity and therefore generally safe to use.
Examples of Alcohols:
| Name | Oils found in | Name | Oils found in |
| linalol | Basil, Bergamot, Cinnamon, Clary Sage, Geranium, Jasmine, Lavender, Lemon, Neroli, Melissa, Nutmeg, Petitgrain, Thyme, Ylang Ylang, Rosemary | citronellol | Melissa, Rose, Geranium |
| nerol | Bergamot, Jasmine, Neroli, Orange, Petitgrain, Rose | nerolidol | Neroli, Pettitgrain |
| terpineol | Bergamot, Geranium, Jasmine, Juniper, Marjoram, Neroli, Nutmeg, Petitgrain, Tea Tree | menthol | Peppermint |
| borneol | Camphor, Ginger, Juniper, Marjoram, Nutmeg, Pine, Thyme, Lavender, Rosemary | farnesol | Jasmine, Petitgrain, Rose, Ylang Ylang |
| geraniol | Geranium, Jasmine, Lavender, Mandarin, Melissa, Neroli, Nutmeg, Petitgrain, Rose, Ylang Ylang |
ALDEHYDES
Aldehydes are antiseptic and often responsible for the scent of a plant. Aldehydes are mainly found in lemon-scented oils such as Lemon, Melissa and Lemongrass.
Examples of Aldehydes:
| Name | Oils found in | Name | Oils found in |
| citral | Ginger, Lavender, Lemon, Mandarin, Melissa, Orange, Petitgrain, Geranium | benzaldehyde | Cinnamon Leaf |
| citronellal | Lavender, Lemon, Mandarin, Melissa, Orange, Eucalyptus | anisic | Sweet Fennel |
| cuminic | Chamomile German, Fennel, Myrrh, Rosemary | furfurol | Cinnamon, Clove Bud, Cypress, Sandalwood |
ESTERS
Esters are scented and often used in perfumes. They have antispasmodic, anti-fungal and sedative properties. There are many Esters but they are usually found in minute amounts within Essential Oils.
Examples of Esters:
| Name | Oils found in | Name | Oils found in |
| geraniol | Lavender, Lemon | geranyl acetate | Melissa, Petitgrain, Lavender |
| methyl anthranilate | Jasmine, Mandarin, Neroli, Orange | terpenyl acetate | Cypress, Pine |
| bornyl acetate | Pine, Rosemary | benzyl acetate | Ylang Ylang |
KETONES
Ketones are toxic and are found in more of the toxic Essential Oils that should not be used for aromatherapy purposes (i.e. Mugwort, Pennyroyal, Thuja, Hyssop, Sage).
These toxic ketones can affect the Central Nervous System and may also cause epilepsy.
Essential Oils that have smaller amounts of Ketones are safer to use, such as Peppermint, Rosemary, Ginger, and can be used to boost the immune system.
Examples of Ketones:
| Name | Oils found in | Name | Oils found in |
| borneone | Basil | camphor | Basil, Camphor, Marjoram, Rosemary |
| cineole | Basil, Clary Sage, Ginger, Peppermint, Eucalyptus, Lavender, Rosemary, Tea Tree | jasmone | Jasmine, Neoli, Peppermint |
| menthone | Peppermint, Geranium | carvone | Peppermint |
PHENOLS
Phenols are weak acids and can be extremely irritating to the skin and mucous membranes. They can also cause damage to the liver if used over a long period of time. Phenols are stimulating, disinfectant and anti-bacterial. Examples of oils containing Phenols include Thyme, Clove Bud, Cinnamon, Nutmeg and these oils are best avoided in massage, or used in very small doses.
Examples of Phenols:
| Name | Oils found in | Name | Oils found in |
| eugenol | Basil, Black Pepper, Cinnamon, Clove Bud, Geranium, Jasmine, Myrrh, Nutmeg, Patchouli, Rose, Ylang Ylang | methylchavicol | Basil, Sweet Fennel |
| safrole | Black Pepper, Cinnamon, Nutmeg, Ylang Ylang | myristicin | Black Pepper, Nutmeg |
| carvacrol | Peppermint, Thyme | yhymol | Thyme |
| ylangol | Ylang Ylang | anethole | Sweet Fennel |
SESQUITERPENES
Sesquiterpenes have generally soothing and anti-inflammatory properties and can be found in Essential Oils such as Chamomile and Lavender.
Examples of Sesquiterpenes:
| Name | Oils found in | Name | Oils found in |
| azulene | Chamomile Roman | artemol | Chamomile Roman |
| caryophyllene | Black Pepper, Clary Sage, Juniper, Lavender, Marjoram, Melissa, Rosemary, Thyme | cadinene | Cedarwood, Frankincense, Juniper, Lavender, Lemon, Myrrh, Patchouli, Peppermint, Pine, Ylang Ylang |
| santalene | Sandalwood | cedrene | Cedarwood |
TERPENES
Terpenes are present in the majority of Essential Oils. They have anti-viral, anti-septic, analgesic properties but some can cause skin irritation or irritation of the mucous membranes. Some oils that contain high amounts of terpenes are Lemon, Orange, Fennel, juniper, Pine, Petitgrain.
Examples of Terpenes:
| Name | Oils found in | Name | Oils found in |
| pinene | Basil, Black Pepper, Cinnamon, Cypress, Clary Sage, Clove Bud, Eucalyptus, Frankincense, Juniper, Lavender, Lemon, Marjoram, Myrrh, Nutmeg, Pine, Rosemary, Tea Tree, Ylang Ylang | sylvestrene | Basil, Cypress, Pine |
| bisabolene | Black Pepper, Lavender, Lemon | dipentene | Bergamot, Cinnamon, Fennel, Frankincense, Lavender, Lemon, Myrrh, Nutmeg, Pine |
| camphene | Black Pepper, Camphor, Cypress, Eucalyptus, Fennel, Frankincense, Ginger, Juniper, Lavender, Lemon, Neroli, Petitgrain, Pine, Rosemary | phellandrene | Cinnamon, Clary Sage, Eucalyptus, Fennel, Frankincense, Ginger, Lavender, Lemon, Peppermint, Pine |
| limonene | Fennel, Ginger, Juniper, Lavender, Lemon, Mandarin, Myrrh, Neroli, Orange, Peppermint, Petitgrain | cymene | Cypress, Thyme, Tea Tree |
| terpinene | Marjoram, Thyme, Tea Tree | sabinene | Juniper, Geranium, Marjoram |
