Introduction to the Eight Classifications of Essential Oil Constituents

Isis Jade


Time to read 4 min

Essential Oil Constituents

Essential Oil Constituents Main Classifications

In general, pure essential oils can be subdivided into two distinct groups of essential oil constituents; the hydrocarbons which are made up almost exclusively of terpenes, which include monoterpenes, sesquiterpenes, and diterpenes), and oxygenated compounds which are mainly esters, aldehydes, ketones, alcohols, phenols, and oxides.

Today we will cover eight of these essential oil constituents classifications in a very high level overview. This is not an in-depth chemistry blog, but giving you some general idea as to how these constituents can be beneficial (or risky) to your health and why it is critical to use properly formulated aromatherapy oils that are lab-tested and certified organic.


Terpenes are essential oil constituents that inhibit the accumulation of toxins and help discharge existing toxins from the liver and kidneys. Here are the basic Terpenes we find in Essential Oil Chemistry.


Sesquiterpenes are antiseptic and anti-inflammatory essential oil constituents.

They work as a liver and gland stimulant and often contain caryophyllene and valencene. 

Research from the universities of Berlin and Vienna show these essential oil constituents increased oxygenation around the pineal and pituitary glands.

Further research has shown that sesquiterpenes have the ability to bypass the blood-brain barrier and enter the brain tissue. 

Other sesquiterpenes, like chamazulene and farnesol, are very high in anti-inflammatory and anti-bacterial activity.

Chamazulene be found in chamomile, tansy, and yarrow. A few sesquiterpenes that are very effective:

  • Farnesene is anti-viral in action.
  • Limonene has strong anti-viral properties and has been found in 90% of the citrus oils.
  • Pinene has strong antiseptic properties and may be found in high proportions in the conifer oils such as pine, fir, spruce, and juniper.
  • Other terpene-based essential oil constituents include camphene, cadinene, cedrene, dipentene, phellandrene, terpinene, sabinene, and myrcene.


Esters are essential oil constituents resulting from the reaction of an alcohol with an acid (known as esterification). 

Esters are some of the most common essential oil constituents and are found in a large number of oils. Esters are anti-fungal, calming and relaxing.

  • Linalyl acetate may be found in bergamot, Clary sage, and lavender
  • Geraniol acetate may be found in sweet marjoram.
  • Other esters include bornyl acetate, eugenol acetate, and lavendulyl acetate.


Aldehydes are highly reactive essential oil constituents and characterized by the group C-H-O (Carbon, Hydrogen, Oxygen). 

In general, these essential oil constituents are anti-infectious with a sedative effect on the central nervous system. 

They can be quite irritating when applied topically (citral being one example), but may have a profound calming effect when inhaled.

  • Citral is very common with a distinctive antiseptic action. It also has an anti-viral application as with melissa oil when applied topically on herpes simplex.
  • Citronellal is also very common and has the same lemony scent as citral. Along with citral and neral, citronellas may be found in the oils of melissa, lemongrass, lemon, mandarin, lemon-scented eucalyptus, and citronella.
  • Elements of these essential oil constituents have also been found in lavender and myrrh. Other aldehydes include benzaldehyde, cinnamic aldehyde, cuminic aldehyde, and perillaldehyde.


Ketones are sometimes mucolytic and neuro-toxic when isolated from other essential oil constituents. 

However, the reality is this: no documented cases exist where whole essential oils with a high concentration of ketones (such as mugwort, tansy, sage, and wormwood) have ever caused a toxic effect on a human being in any research study to date. 

In addition, an enormous amount of these oils would have to be consumed for them to result in a toxic neurological effect.

Ketones are essential oil constituents that stimulate cell regeneration, metabolism, promote the formation of healthy tissue, and liquefy mucus and phlegm.

Ketones are helpful with such conditions as dry asthma, colds, flu and dry cough and are largely found in oils used for the upper respiratory system, such as hyssop, Clary sage, and sage.

  • Thujone is one of the most "risky" members of the ketone family. It can be an irritant and upsetting to the central nervous system and can be neuro-toxic when taken internally. Although it may be inhaled to relieve respiratory distress and my stimulate the immune system, it should only be administered by an educated and professional aromatherapist at the dilution rates for application are 1%. 
  • Jasmone (found in jasmine) and fenchone (found in fennel) are both non-toxic.
  • Other ketones include camphor, carvone, menthone, methyl nonyl ketone, and pinacamphone.


Alcohols are commonly recognized essential oil constituents for their antiseptic and anti-viral activities. They create an uplifting quality and are generally regarded as non- toxic.

  • Terpene Alcohols stimulate the immune system, work as a diuretic and a general tonic, and are anti-bacterial as well.
    • Linalol can help relieve It may be found in rosewood and lavender.
    • Citronellol may be found in rose, lemon, eucalyptus, geranium, and others.
    • Geraniol may be found in geranium as well as
    • Farnesol may be found in It is also good for the mucous.
    • Other terpene alcohols include borneol, menthol, nerol, terpineol, (which Gattefosse considered to be a decongestant), vetiverol, benzyl alcohol, and cedrol.

  • Sesquiterpene Alcohols are anti-inflammatory, anti-bacterial, anti- mycotic, and ulcer-protective (preventative).
    • Bisabolol is one of the the strongest sesquiterpene It may be found in chamomile oils where it also functions well as a fixative.


Phenols are generally responsible for the overall fragrance of an oil. These essential oil constituents are antiseptic, anti-bacterial, and strongly stimulating but can also be quite caustic to the skin. They contain high levels of oxygenating molecules and have antioxidant properties.

  • Eugenol may be found in clove and cinnamon
  • Thymol is found in thyme essential oil and may not be as caustic as other phenols.
  • Carvacrol may be found in oregano and Research has shown it to contain anti-cancerous properties.
  • Others in the phenol family include methyl eugenol, methyl chavicol anethole, safrole, myristicin, and apiol.


Oxides an oxide is "a binary compound of an element or a radical with oxygen". These essential oil constituents can work synergistically, enhancing other constituents actions. 

  • Cineol (or eucalyptol) is by far the most important member of the family and virtually exists in a class of its own. It is anesthetic, antiseptic, and works as an expectorant. Cineol is well known as the principal constituent of eucalyptus oil. It may also be found in rosemary, cinnamon, melissa, basil, and ravensara.
  • Other oxides include linalol oxide, ascaridol, bisabolol oxide, and bisabolone oxide.

Leave a comment