The chemistry of essential oils, and their chemical componen

Most people either use essential oils for their therapeutic effect or for the fragrance alone but it is also interesting to take note of the chemistry, of which the oils are made up from.

It is interesting to know the chemical components that nature combines to make up the oils, but it is also humbling to take note of the fact that even with the best human efforts, should you in a laboratory combine all the chemicals in the correct proportions, you would still not have an identical oil.

Such a copy of an oil will not have the same therapeutic effect as the natural and pure essential oil. And though we pride ourselves on being a technology advanced society, modern science can still not unlock the secrets of essential oils and why they can do what they do.

If you for instance took all the correct chemical components, which will include lavandulol, borneol, terpineol, geraniol and linalol, and try to make up lavender essential oil in a laboratory, you will not have an oil that can successfully treat burns the way that true lavender oil can.

Essential oils, like all organic compounds, are made up of hydrocarbon molecules and can further be classified as terpenes, alcohols, esters, aldehydes, ketones and phenols etc.

To help you in the understanding of the chemical constituents of the oils, it may be a good idea just to have a look at what an isoprene unit is.

Every single oil normally has more than a hundred components, but this figure can also run into thousands, depending on the oil in question.

When you analyze essential oils with a chromatograph various organic components are found and the primary ones are as follows:

• Terpene hydrocarbons

  • Monoterpene hydrocarbons

  • Sesquiterpenes

• Oxygenated compounds

  • Phenols

  • Alcohols

    • Monoterpene alcohols

    • Sesquiterpene alcohols

  • Aldehydes

  • Ketones

  • Esters

  • Lactones

  • Coumarins

  • Ethers

  • Oxides

• Terpenes Hydrocarbons: 
  • Monoterpene
    • These monoterpene compounds are found in nearly all essential oils and have a structure of 10 carbon atoms and at least one double bond. The 10 carbon atoms are derived from two isoprene units.
    • They react readily to air and heat sources. For this reason citrus oils do not last well, since they are high in monoterpene hydrocarbons and have a quick reaction to air, and are readily oxidized.
    • Although some quarters may simply state that these components have anti-inflammatory, antiseptic, antiviral and antibacterial therapeutic properties while some can be analgesic or stimulating with a tonic effect, it could be seen as a very broad generalization, since this large group of chemicals vary greatly. Since some have a stimulating effect on the mucus membranes they are also often used as decongestants.
  • Sesquiterpenes
    • These sesquiterpenes consist of 15 carbon atoms and have complex pharmacological actions and here we can look at chamazulene, which is found in German chamomile.
    • It has anti-inflammatory and anti-allergy properties. Another sesquiterpene often found in chamomile and rose, as well as other floral oils is farnesene.
    • History highlight of terpene research
    • The 1910 Nobel prize winner for Chemistry was Professor Otto Wallach for his work on terpenes which influenced the essential oil industry. 
• Oxygenated compounds: 
  • Phenols
    • The phenols found in essential oils normally have a carbon side chain and here we can look at compounds such as thymol, eugenol and carvacrol. These components have great antiseptic, anti-bacterial and disinfectant qualities and also have greatly stimulating therapeutic properties.
    • Due to the nature of phenols, essential oils that are high in them should be used in low concentrations and for short periods of time, since they can lead to toxicity if used over long periods of time, as the liver will be required to work harder to excrete them.
    • Phenols are also classified as skin and mucus membrane irritants and although they have great antiseptic qualities, like cinnamon and clove oil, they can cause severe skin reactions.
  • Alcohols
    • Monoterpene alcohols
      • These oils have good antiseptic, anti-viral and anti-fungal properties with very few side effects such as skin irritation or toxicity and have an uplifting energizing effect.
      • Examples of these alcohols are linalool, citronellol and terpineol found respectively in lavender, rose and geranium, and in juniper and tea tree oil.
    • Sesquiterpene alcohols
      • These alcohols are not commonly found in essential oils, but when found, like bisabolol in German chamomile, have great properties, which include liver and glandular stimulant, anti-allergen and anti-inflammatory.
      • Other oils that contain sesquiterpene alcohols are sandalwood (a-santalol) as well as ginger, patchouli, vetiver, carrot seed, everlasting and valerian.
• Aldehydes 
  • These aldehydes have anti-fungal, anti-inflammatory, disinfectant, sedative yet uplifting therapeutic qualities and are the component that imparts the citrus-like fragrance in melissa, lemongrass and citronella. These properties are best used in aromatherapy when the essential oil is used in low dilutions - around 1%.
  • Should oils high in this component be used, it could cause skin irritation and sensitivity as for instance lemongrass oil. Aldehydes are also unstable and will easily oxidize in the presence of oxygen and even low heat.
• Ketones
  • Although ketones can be toxic, as in the case of thujone found in thuja and wormwood oil as well as pinocamphone found in others, they also have some great therapeutic benefits - especially in the field of easing the secretion of mucus as well as cell and tissue regeneration.
  • Other oils, such as hyssop, eucalyptus and rosemary have moderate amounts of ketones, and when used properly in aromatherapy can be greatly beneficial to the body.
  • The ketone italidone found in everlasting, not only has the mucolytic (mucus easing) properties, but is also useful in skin regeneration, wound healing and reducing old scar tissue such as in wounds, stretch marks and adhesions.
  • Essential oils high in ketones need to be used with care in pregnancy.
• Esters
  • Esters are formed from alcohols and acids, and are named after both their original molecules with the alcohols dropping the "ol" and gaining an "yl" and the acids dropping the "ic" and gaining an "ate".
  • The esters found in essential oils are normally very fragrant and tend to be fruity and their therapeutic effects include being sedative and antispasmodic. Some esters also have anti-fungal and anti-microbial properties - like the anti-fungal properties in geranium oil.
  • The most well known ester must be linalyl acetate, which is found in lavender, clary sage as well as petitgrain.
  • These components are normally gentle in their actions and can be used with great ease.
• Lactones and coumarins 
  • Lactones contain an ester group integrated into a carbon ring system and coumarins are also types of lactones. There are similarities between the actions of lactones, coumarins and ketones since they also have some neurotoxic effects and can cause skin sensitizing and irritation.
  • Yet the sesquiterpene lactone, called helenalin found in arnica oil, seems to be responsible for the anti-inflammatory action of arnica oil.
  • The amount of lactones and coumarins normally found in essential oils is very low, and does not pose a huge problem. Lactones also have great mucus moving and expectorant properties and for this reason elecampane is often used in the treatment of bronchitis and chest complaints.
  • Some coumarins, like furocoumarin - bergaptene - found in bergamot oil are severely skin UV sensitive and should be used with great care should you be exposed to sunlight. 
• Ethers
  • Phenolic ethers are the most widely found ethers in essential oils with anethol found in aniseed, the only real ether of importance together with methyl chavicol found in basil and tarragon.
• Oxides 
  • The main therapeutic effect of oxides are that of expectorant, with 1,8-cineole - commonly known as eucalyptol being the most well known.

The above is a brief overview of the chemical components found in essential oils, and should not be seen as a lesson in organic chemistry, but was merely included for the sake of interest.