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The chemistry of the oil dictates the properties, so learning more about the chemistry side of things also provides you with a better understanding of why some oils might have more safety considerations attached to them than others.
It could be said that chemistry takes away from the intuitive side of aromatherapy but in fact the opposite is true. By contrast, recognising the chemical patterns enhances most people’s essential oil journeys and helps them to get even more from their oils and to incorporate them more fully into their everyday lives.
IMPORTANT NOTE: We are only talking about the general chemical families and their properties in this post. We make no claims as to how to obtain any of the properties mentioned from the chemical families, under what conditions, from what products, or in what doses, or even if the desired properties can be obtained at all in humans. The fact that certain essential oils contain these constituents in no way means that we are claiming that the essential oil product has any specific medicinal or therapeutic properties.
It All About The Molecules
Essential oils are made up of molecules but let’s starts small and begin with the question…
“What on Earth is a molecule?”
You can consider these as the smallest component parts that make up the oils.
Everything in the world and the universe is composed of matter, which by definition is anything that takes up space, has mass, and can be perceived by the senses. Three main phases of matter exist: solid, liquid, and gas.
All matter is composed of elements.
A single unit of an element is called an atom.
At the center of an atom is a core called a nucleus that is composed of two types of subatomic particles: protons (positively charged particles) and neutrons (neutrally charged particles). Atoms are considered electrically neutral because they also have negatively charged subatomic particles called electrons that circle around the atom’s nucleus. The charges of the protons and the electrons balance each other ensuring that the atom has no overall charge. Sometimes, an atom will gain or lose electrons, giving it an imbalanced number of protons and electrons. When this occurs, that atom has a charge and is called an ion.
All living things are made of molecules arranged in many different ways.
For the most part these will be either chains of molecules, or rings, or a combination of the two. They comprise of carbon, hydrogen and oxygen.
We call these the chemical constituents or components (both the words ‘constituents’ and ‘components’ are often used by people to describe the same thing). Similar groups of molecules are categorised together in “families”
Each family has its own traits, properties and benefits. They have certain fragrance profiles – because of how they developed in the plant.
Based on how we understand the family to work in the human body, will also give us clues about any safety concerns we might need to be aware of.
What exactly is an essential oil?
Understanding why the plant originally developed the chemicals helps us to comprehend the properties of the oil further. So let’s start there.
Did you know a plant does not need the essential oil to live?
No?
Weird, huh?
In fact, the more correct terms for the chemicals found in your bottle is Secondary Metabolites.
The plant has strangely developed these as a method of making its life easier once is starts growing. Based on the “Character” or “Personality” of the plant, it will evolve these chemicals, internally to do many different things.
Some, it creates as a means of attracting pollinators, others happen because it is living in a very cold or hot place so it needs to create a temperature control. Some are created to pour into the soil, to prevent any other seeds from germinating. Many are manufactured by the plant as a response to some kind of mould or fungus, to heal tissues that have been munched by insects, or even to repel the critters from doing it again.
Top notes and base notes
Now, imagine you are opening a bottle of essential oil. Molecules literally burst out of the bottle and evaporate. We call this volatility. Those molecules that drift into the air, are the same as erupted from the plant and we call these aromatic volatiles.
Some molecules are more volatile than others. Light (as in weight) ones drift off like fairy wings and heavier ones, which take longer to evaporate, will be slower to move and therefore take much longer.
If we are blending the oils, these very light molecules tend to make up oils we know as top notes and the base notes are rich in molecules which are much heavier.
Mass Spectrometry report
The Gas Chromatography and Mass Spectrometry report tells you what chemical constituents can be found in each oil.
Oil from the same plant species can vary greatly in chemical composition, scent and therapeutic properties based on the country and even region they have been sourced from.
Like your favourite bottle of wine, soil and conditions the plant has been grown in makes a huge difference to the essential oil. For that reason you might find certain countries are favoured for certain oils. This does not necessarily mean they are better or worse as an oil per se, but that they have properties that make them better for a particular condition.
Geographic origin of DoTerra essential oils
Two oils from the same producer may even vary from season to season. Things like the weather and climate conditions, how it’s grown, condition of the soil, when it’s harvested, precipitation levels, and harvesting technique, the distillation all contribute to the chemical
Alterations to any of these factors can influence the chemical profile of an essential oil, and in turn diminish or enhance their beneficial properties.
Steam distillation, expression (also known as cold pressing), and solvent extractions are widely used in the essential oil industry today because of their demonstrated ability to produce oils of therapeutic quality.
Each batch of oil should be thoroughly tested for potency and purity using a complex standard of quality testing procedures. To maintain the quality of the product, essential oils should be securely packaged in glass bottles and stored away from direct sunlight or temperature extremes.
So, this is why we believe every batch of essential oil produced should have its chemistry analysed. That way the consumer knows exactly what they are buying and the properties that each particular bottle of oil will have.
Why I choose DoTerra?
DoTerra Certified Pure Therapeutic Grade (CPTGTM) are beyond organic, verified pure, free of fillers, pesticides, and foreign contaminants.
Understanding essential oil synergy
The chemical profile of essential oils is very complex containing up to hundreds of individual constituents.
Most oils will have some of each different chemical family contained within their make-up. Their own plant family often dictates what the predominant chemical family might be.
Instead of side effects, essential oils have many main effects.
This happens because of this beautiful cocktail of different chemicals all interacting together. These chemicals also support and moderate each other. This results in an essential oil having many different properties.
We call this interaction synergy.
Several studies have been conducted examining both the synergistic action of the whole oil as well as the individual action of isolated constituents. These studies have verified that there is increased benefit and safety from using the whole oil, rather than just an individual constituent. In other words, oils are best used in their whole form—with the exact composition designed by nature—nothing added, removed, or isolated.
Potency
The Chemical Families
Essential oils are made up of carbon and hydrogen (hydrocarbons). The main ‘building block’ of how the hydrogen and carbon molecules are arranged together is called an isoprene. Many sets of isoprenes, categorised by similarity of how each set is built, are known as Families.
Similar arrangements result in similar properties.
The most commonly found classes of essential oil constituents are:
- Monoterpenes
- Sesquiterpenes
- Diterpenes
- Alcohols
- Phenols
- Aldehydes
- Ketones
- Esters
- Oxides
MONOTERPENES
This is the largest chemical family and the constituents from this family are found everywhere in nature. Made up of hydrogen and carbon molecules called hydrocarbons, they contain just 10 carbon atoms.
When a chemical bond forms between two isoprene units, a 10-carbon molecule called a monoterpene results. Monoterpenes can assume many shapes including cyclic, straight, and branched varieties. Common physical characteristics of monoterpenes are a low molecular weight (meaning they are small and light compared to other types of molecules), clear in color, free flowing (not viscous), high volatility, and strong aroma. You will see below that monoterpenes are present in varying amounts in nearly every essential oil! Common monoterpenes found in essential oils are limonene, pinene, terpinene, and cymene.
- Cleansing1
- Antioxidant2*
- Protective to cells and promotes normal cell growth3*
- Repels insects4
- Stimulating and enhancing effects on mood and cognitive health5
| Essential Oil | Main Monoterpene Constituent (s) | Amount |
| Grapefruit5 | limonene | Approximately 97% |
| Wild Orange1,5 | limonene | Approximately 95% |
| Lemon1,5 | limonene, pinene | Approximately 95% |
| Lime1,5 | limonene, terpinene | Approximately 85% |
| Frankincense3*,5 | pinene, limonene | Approximately 75% |
| White Fir5 | limonene, pinene | Approximately 75% |
| Juniper Berry1,5 | pinene, sabinene, myrcene | Approximately 75% |
| Cypress5 | pinene, carene | Approximately 70% |
| Bergamot1,5 | limonene, terpinene | Approximately 50% |
| Black Pepper2*,5 | limonene, carene | Approximately 50% |
| Coriander5 | pinene, terpinene | Approximately 45% |
| Dill1,5 | limonene, phellandrene | Approximately 40% |
| Rosemary4,5 | pinene, camphene | Approximately 35% |
| Melaleuca1 | terpinene | Approximately 35% |
| Marjoram5 | terpinene | Approximately 30% |
| Fennel5 | limonene | Approximately 25% |
Top notes are rich in monoterpenes. Their fragrance dissipates quickly. If you use these in a diffuser, they disappear almost immediately.
An example of a monoterpene is d-limonene found in most citrus oils. This constituent gives these oils their lemony, fresh zing.
Shelf life: 6 months – 3 years. Store in a cool, dark place to help prolong their shelf life.
Safety: Consult with your doctor before use. Can be irritating to the skin, especially if older/oxidised. Do not wear in direct sun.
SESQUITERPENES
Like monoterpenes, these contain only hydrogen and carbon (hydrocarbons) but sesquiterpenes have 5 more carbons (so in total 15 carbons or 3 isoprene chains)
Because of their higher molecular weights, sesquiterpenes are less volatile than monoterpenes, and are therefore less prevalent in essential oils overall; however, they have unique properties that distinguish them from monoterpenes and make them important contributors to the synergistic functionality of essential oils. Common sesquiterpenes found in essential oils are cedrene, zingiberene, himachlene, and caryophyllene.
Main Health Effects:
- Cleansing1
- Digestive health2*
- Aides in healthy circulation3*
- Improves the appearance of skin4
- Promotes grounding, sedative and hormonal balancing (Oils taken from the roots of plants tend to be high in this group and as such they act as if they are anchoring you more)
| Essential Oil | Main Sesquiterpene Constituent(s) | Amount |
| Cedarwood4,5 | cedrene, thujopsene | Approximately 70% |
| Patchouli4,5 | bulnesene, guaiene | Approximately 65% |
| Vetiver5 | vatirenene, seychellane, cubebene | Approximately 65% |
| Ginger2*,5 | zingiberene, sesquiphellandrene, curcumene | Approximately 55% |
| Ylang Ylang5 | germacrene, caryophyllene, farnesene | Approximately 55% |
| Myrrh1,2*,4,5 | myrrh sesquiterpenoid, elemene | Approximately 55% |
| Helichrysum4 | himachalene, curcumene | Approximately 40% |
| Melissa5 | germacrene, caryophyllene | Approximately 40% |
| Black Pepper3* | caryophyllene | Approximately 25% |
Shelf life: Some can last as long as 6-8 years shelf life. They evaporate much slower meaning they have a much longer shelf life.
Research shows these are able to cross the blood brain barrier affecting the brain, emotions and hormones, and we use these as very sedative and pacifying oils.
Safety considerations: Consult with your doctor before use.
Alcohols
Main Health Effects of alcohols
- Powerfully cleansing, protects against environmental threats1
- Uplifting effects on mood2
- Supports restful sleep3
- Supports a healthy cardiovascular system4*
| Essential Oil | Main Alcohol Constituent(s) | Amount |
| Sandalwood2,3 | santalol | Approximately 90% |
| Basil2 | linalool | Approximately 80% |
| Rose2 | citronellol, geraniol, nerol | Approximately 60% |
| Marjoram 2,4* | linalool, terpinenol | Approximately 55% |
| Geranium2 | citronellol, geraniol | Approximately 50% |
| Melaleuca1 | terpineol | Approximately 50% |
| Peppermint2 | menthol | Approximately 50% |
| Cilantro1 | linalool, decenol | Approximately 45% |
| Jasmine2 | phytol, linalool | Approximately 45% |
| Lavender2,3 | linalool | Approximately 35% |
| Coriander2 | linalool, geraniol | Approximately 30% |
| Clary Sage2,3 | linalool | Approximately 25% |
| Patchouli2 | patchoulol | Approximately 25% |
| Cedarwood2 | cedrol | Approximately 20% |
Shelf life: 3-5 years
Safety: Consult with your doctor before use. Generally safe on the skin but menthol can be irritating. Some of the alcohols are not recommended for young children under 5.
Phenols
Terpenes use combinations of isoprene chains (5 carbon chains) but phenols also have ‘side chains’ which are incomplete sets of 5 carbon units in a chain which makes them more unpredictable.
Main Health Effects:
- Protects against environmental threats1
- Antioxidant2*
- Repels insects3
- Strongly antibacterial
- Strong antiseptic
- Strongly antimicrobial
- Strongly antiviral
- Antifungal
- Rubefacient (stimulates blood and oxygen circulation to an area)
- Stimulant
Oils containing phenols
- Clove
- Thyme CT Thymol
- Oregano
- Cinnamon leaf
- Holy Basil
| Essential Oil | Main Phenol Constituent(s) | Amount |
| Oregano1,2* | thymol, carvacrol | Approximately 90% |
| Clove2*,3 | eugenol | Approximately 80% |
| Thyme1,3 | thymol, carvacrol | Approximately 50% |
Average shelf life: 3-5 years
General safety considerations: Consult with your doctor before use.
This “untidiness” of the chemical structure means that the compound is not as stable, is chemically hot and irritating and with many safety considerations to think about when using phenolic oils.
We use these in very low strength dilutions, use them sparingly, and in small discrete areas to check sensitivity.
Many phenols thin the blood, so when mixed with prescription drugs, this can be dangerous.
Only use phenolic oils, in any capacity, for short periods of time and in very weak dilutions. It is recommended to double the dilution to 2 tbsp of fractionated coconut oil to 1 drop of essential oil.
The body is not very adept at ridding itself of phenols so they can linger in your system for a while and as such, begin to create a build up. For this reason, prolonged use of this group leads to sensitisation.
ALDEHYDES
Main health effects:
- Protects against environmental threats1
- Calming to the emotions2
- Helps support healthy gastrointestinal function and digestion3*
| Essential Oil | Main Aldehyde Constituent(s) | Amount |
| Cassia1,2 | cinnamaldehyde, benzaldehyde | Approximately 90% |
| Lemongrass3* | geranial, neral | Approximately 75% |
| Cinnamon1 | cinnamaldehyde | Approximately 70% |
| Cilantro3* | decenal | Approximately 45% |
| Melissa1,2 | geranial | Approximately 35% |
Shelf life: 6 months to 3 years
Safety considerations: Consult with your doctor before use.
Ketones
Ketones need to be treated with caution because they can be quite harsh on the body. The Federation of Aromatherapy has a number of oils listed as hazardous and many of these are due to the high ketone content.
Main Health Effects for ketones (in low concentrations)
- Improves the appearance of skin1
- Some have calming properties2
- Supports healthy respiratory function3*
- Promotes healthy digestion4*
Oils containing ketones
- Peppermint
- Rosemary
- Rock Rose
- Sage (Spanish)
- Spearmint
- Spike Lavender
- Turmeric
- Valerian (Root)
- Vetiver
| Essential Oil | Main Ketone Constituent(s) | Amount |
| Dill2,4* | carvone | Approximately 50% |
| Peppermint 3*,4* | menthone | Approximately 15% |
| Rosemary 2,3*,4* | camphor | Approximately 10% |
| Fennel 2,3*,4* | frenchone | Approximately 5% |
| Lavender 1,2 | octanone | Approximately 5% |
Shelf life: 3-5 years
Safety considerations: Consult with your doctor before use.
Research demonstrates that diabetics should avoid high levels of ketones as when insulin is interrupted, ketone levels can be extremely high
Rosemary, camphor and hyssop are three examples of oils containing ketones that are neurotoxic to the CNS. These should be avoided by people with epilepsy and other mental health conditions.
Esters
Esters are created when acids and alcohols combine. They are characterised by a fruity aroma.
Esters are good to turn to when you are looking for deep relaxation, stress relief or before you go to bed.
Main Health Effects:
- Calming, relaxing, soothing, and balancing effects on mood1
- Reduces the appearance of skin blemishes2
- Provides a soothing and warming sensation when applied topically3
- Respiratory stimulants
- Decongestant and mucolytic
- Mentally stimulating
| Essential Oil | Main Ester Constituent(s) | Amount |
| Birch3 | methyl salicylate | Approximately 99% |
| Wintergreen 1,2,3 | methyl salicylate | Approximately 99% |
| Roman Chamomile 1,2 | isobutyl acetate, isoamyl angelate, | Approximately 75% |
| Clary Sage 1 | linalyl acetate | Approximately 65% |
| Lavender 1,2 | linalyl acetate | Approximately 50% |
| Helichrysum 1,2 | neryl acetate | Approximately 40% |
| Bergamot 1,2 | linalyl formate | Approximately 40% |
| Jasmine 1,2 | benzyl acetate, benzyl benzoate | Approximately 40% |
- Shelf life: 3-5 years
- Safety considerations: Consult with your doctor before use.
- Thins the blood and can increase the effect of other blood thinning medications so should be avoided by anyone taking these medicines.
- Avoid topical use with damaged skin. Always check the safety recommendations for the individual oil you plan to use
OXIDES
Oxides are ethers where the oxygen atom forms part of a ring in cyclic form. The most well known in aromatherapy tending to be 1,8-cineole (eucalyptol)
Oxides Main Health Effects:
- Protects against environmental threats1
- Promotes feelings of clear breathing2
- Supports healthy respiratory function3*
| Essential Oil | Main Oxide Constituent(s) | Amount |
| Eucalyptus 1,2 | eucalyptol | Approximately 75% |
| Rosemary 3* | eucalyptol | Up to 40% |
| Peppermint 3* | eucalyptol | Up to 10% |
| Thyme 1 | eucalyptol | Up to 10% |
Oils containing high levels of oxides
- Cardamom
- Eucalyptus Globulus, Blue Mallee & Radiata
- Fragonia
- Laurel Leaf
- Spike Lavender
- Ravintsara
- Rosalina
- Rosemary
Safety considerations: Consult with your medical Doctor before use.
- Can be irritating to the skin and sensitizing if oxidized
- 1,8-cineole rich oils should be avoided around young children and people who suffer from asthma ie. rosemary, basil, eucalyptus oil.
Conclusion
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This is just a general crash course in essential oil chemistry to help you better understand and use essential oils in your day to day life. Remember that even though I hope this post has been helpful to you, the generalisations in this post are only scratching the surface of aromatherapy and essential oil chemistry.
Even the trace constituents in an oil can dramatically contribute to the pharmacological activity and the dominant constituents don’t always cause the strongest effects. One example is orange oil which is around 95% d-limonene, but it is the 5% of other constituents that work together to create the main fragrance.
Lots of individual constituents within each family also come with individual properties or may react in different ways when blended together and biologically (different reactions can be seen depending on how the oil is used and in different individuals)… and this is before we even consider emotional, mental and other factors in a more holistic view.
New research is coming out all the time – so by all means use this as a starting point, but know that generalisations are not the most accurate or ideal way to approach things, so always try and look up the individual constituents, never stop learning and always be experimenting on your wonderful and exciting essential oil journey.
References:
- A Complete Guide To Aromatherapy – Salvatore Battaglia
- Essential Oil Safety – Tisserand & Young (second edition)
- The Complete Guide To Clinical Aromatherapy & Essential Oils For The Physical Body – Elizabeth Ashley
- Aromatherapy For Health Professionals – Shirley & Len Price (fourth edition)
- Advanced Aromatherapy – Kurt Schnaubelt
- https://www.doterra.com/US/en/essential-oil-organic-chemistry-molecular-structures
Further Reading
- Bowles. J – The basic chemistry of aromatherapeutic essential oils
- Clarke. S – Essential chemistry for safe aromatherapy
- Williams. D – The chemistry of essential oil
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