The Chemistry Of Aromatherapeutic Oils

For too long, the chemistry of aromatherapeutic oils many aromatherapists sigh with despair. Any good school teaches this as a separate module and it is really useful to enable you to make good choices.

This does not apply to fragrance oils at all even though many fragrance oils will contain many of these ingredients. If you prefer to use only fragrance oils, this is not the blog you need.

When you see the gas chromatography results for the chemistry of aromatherapeutic oils, the list or aromatic molecules and chemical compounds can appear daunting at first, but we can break this down into general groups that make it easier to understand.


Esters give off a very fruity aroma and are known for inducing deep relaxation and stress relief. They tend to be very gentle on the skin (as long as the skin is not broken) and they can thin the blood so contraindications should always be taken note of. They are generally antifungal, antimicrobial and antispasmodic.

Oils that are typically rich in esters are Lavender (especially high altitude Lavender), Ylang Ylang, Rose Geranium and Roman Chamomile. The specific ester molecules usually end in “ate” so the predominant ester in Lavender is Lavandulyl Acetate and the predominant ester in Geranium is Geranyl Acetate.

Ethers and Oxides

Ethers and Oxides are similar with the most well known oxide being 1,8-cineole. Generally, they are good decongestants and good at shifting mucous. They are respiratory stimulants and are mentally stimulating.

Oils that are higher in Ethers are Aniseed, Nutmeg, Sweet Basil and Sweet Fennel. As a side note, nutmegs in some prison kitchens are counted and restricted as some inmates were snorting grated nutmeg to get high. The Myristicin and Elemicin  molecules are psychotropic but they also cause extensive neurological damage.

Oils that are higher in Oxides are Fragonia, Rosalina, Cardamom, Eucalyptus Globulus and Ravintsara, which contains 1,8-cineole.


Aldehydes are mostly fresh and uplifting, often zesty. Interestingly, they can be soothing as well as uplifting at the same time. They do have  high potential for skin irritations and allergic reactions which is why essential oils that are high in this group are often restricted or recommended to be used at lower, safe amounts. They are usually antifungal, anti-inflammatory and disinfectant.

Essential oils notable for their Aldehyde content are Lemongrass, Citronella and Lemon Eucalyptus. 


Terpenes are a large group and are generally light in weight so they dissipate quickly, forming what is often called the top note or the molecules that you smell first.


Monoterpenes are part of the larger Terpenes family and make up a large part of an essential oil. They penetrate the skin easily (diluted of course) and are generally very fragrant, analgesic, antibacterial, antiseptic, anti-inflammatory, antiviral,  decongestant, rubefacient and stimulating. 

Essential oils that contain significant amounts of Monoterpenes are all the citrus oils, Juniper Berry, Cypress, Tea Tree and Rosemary.


Sesquiterpenes are part of the Terpenes family and are a larger molecule and a little heavier so that take longer to be noticed in the fragrance but they cross the blood / brain barrier very easily affecting the mood, emotions and some brain function. Often, they are used for their sedative and calming effects. They are generally antibacterial, analgesic, anti-inflammatory, antiseptic and help wounds to heal quicker. They can be very grounding and balancing. Azulene is a sesquiterpene.

Oils that contain noticeable amounts of Sesquiterpenes are Cedarwood (the Sesquiterpene is Cedrene), Patchouli (Patchoulene), Vetiver, Manuka and Myrrh.


Alcohols which are naturally occurring in the plant and are often specific to the plant. They are another large group which breaks down into smaller groups


Monoterpenols are part of the Alcohols family and can be very reactive with oxygen and lose fragrance easily. This can be an advantage as much as a disadvantage. They are generally antibacterial, anti-inflammatory, antifungal, antimicrobial, antiseptic and antiviral. On the whole, this group is considered to be uplifting and generally very desirable in skincare products.

Oils with noted amounts of Monoterpenols are Palmarosa, Petitgrain, Neroli, Peppermint and Clary Sage.


Sesquiterpenols are part of the Alcohols family and are generally anti-inflammatory, grounding, immune stimulating, sedative and on the whole desirable molecules for skin care products.

Oils with a good Sesquiterpenol content are Sandalwood, Carrot Seed, German Chamomile and Ginger.


Ketones need to be treated with great care. They penetrate into the body very easily and can complicate diabetes and bleeding. It is very much dependent on the amount in the oil, which particular ketone and where it is applied at what percentage. Again, this is why safety notes should be read and taken heed of. Generally, they are good for healing scar tissue, cooling and effective mucolytics and expectorants.

Oils with Ketone levels to be aware of are Spearmint, Spike Lavender, Peppermint and Rosemary. The Ketones usually end in “one” with Carvone in Spearmint, Verbenone in Rosemary and Menthone in Peppermint.


Phenols can evaporate slowly which gives them longer to penetrate into the skin. This can be good or bad depending on the circumstances. You may want this effect of a sore muscle area but you would not want phenols to cling to your nasal mucous membrane if you sniffed the oil or used them in the bath. There are often warnings with oils that contain phenols as many can thin the blood which may cause problems with clotting. They can linge in the system for some time and also start to build up. They are generally strongly antibacterial, antifungal, antimicrobial, antiseptic, antivital, rubefacient and stimulant.

Oils that contain Phenols are Clove (Eugenol), Cinnamon Leaf, Oregano (Carvacrol) and Thyme Thymol). The Ketone often ends in “ol”.

Lactones and Coumarins

Lactones and Coumarins are another group that needs to be used with caution as they can be neurotoxic, irritating and sensitizing. Fortunately, the level of these in essential oils is extremely low because the molecules are quite heavy and don’t often transfer through the steam distillation process. That is why a good supplier checks the gas chromatography of each batch produced. Because of this, it is sometimes absolutes that will contain higher levels because of the production process. Lactones ease congestion and are effective mucolytics while furocoumarins are sedative. The furocoumarins can also cause photosensitivity.

The Lactone molecule tends to end in “ine” or “one” such as Jasmine where the Lactone is Jasmone. In Massoia Bark Oil, the Lactone content is so high that it should never be used on the skin and just used in a diffuser instead.

Oils that contain Coumarins are Bergamot although frequently the furocoumarins that cause the photosensitivity have been removed and it will be labelled as FCF (Furocoumarin Free).

Essential Oil Basics & Adverse Effects

Always read about the essential oil you want to use and check for contraindications so that you use it safely. Do not use aromatherapy oils undiluted. Always dilute them with a vegetable oil and use just a few drops to start with. I hope this has demystified the chemistry of aromatherapeutic oils to a good extent.

Cannabis contains a lot of Terpenes and if you are interested in using cannabis in skincare products, this book will show you how to create a range of high end reams, lotions, butters and gels all using infused cannabis.

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1 thought on “The Chemistry Of Aromatherapeutic Oils”

  1. Being self taught, I had never really grasped the relevance of the breakdown of essential oils and why, if two are safe separately, how they could become unsafe if mixed together. I now get it. Thanks for this.


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