Essential Oil Chemistry

Using essential oils
+Dry Evaporations
+Steam Inhalations
+Showering and Bathing
Follow-up Post: 26 essential oils

If you need a list of plant terms, check out this post.
If you want to jump right into the 26 must have essential oils for you home, check out this post.

Some, but not all plants produce essential oils. Essential oils are concentrated, potently aromatic volatile oils made by plants for a number of reasons, including self-protection, attracting pollinators and adapting to their environment. Essential oils are present in varying amounts in different plants. Some give great volumes (peppermint, rosemary, citrus fruits) and others give very little (rose and neroli). The price of a bottle of Essential oil will often indicate the yield of the plant. Some of the more expensive essential oils have therapeutic applications that a cheaper oil is just as good at helping. There are a few key uses where a more expensive essential oil would be worth a few drops and the price tag.


The chemistry of an essential oil is as unique as it is in a herb, with each oil having its own unique chemical make-up which contributes to that oil’s unique set of therapeutic actions. Each class of chemicals also has a set of therapeutic actions associated with the molecules within that chemical set. We can study an essential oil’s active constituents in the same way they would a herb’s to get an idea about what actions that oil might have. In addition to the plethora of physical effects an essential oil can have on the body, it’s crucial to remember that essential oils, via stimulation of the olfactory bulbs, communicate directly with the limbic system, the seat of our emotions. This gives essential oils a huge healing scope in terms of our emotions and mood, and research has demonstrated time and time again that just smelling certain essential oils can reduce feelings of tension and anxiety. We are aware of the impact carefully chosen essential oils can have on managing stress, tension, anxiety and low mood.

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A class of natural products consisting of compounds with the formula (C5H8)n. These form the major constituents of essential oils. They are responsible for the fragrance, taste, and pigment of plants. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes are further classified by the number of carbons: monoterpenes (C10), sesquiterpenes (C15), etc. (source)

Therapeutic effects include:

  • Antiplasmodial
  • Antimalarial
  • Antiviral
  • Antidiabetic
  • Anticarcinogenic
  • Antioxidant
  • And many, many more

Plants high in Terpenes include tea, thyme, cannabis, sage, pine, turmeric, curcumin, and citrus fruits.

Terraced fields of tea is a traditional landscape of Japan (source)

Different types of terpenes and their properties

ClassificationCarbon atomsSpecies produced fromMedicinal usesReferences
MonoterpenesC10Quercus ilexFragrances, repellentLoreto et al. (2002)
SesquiterpenesC15Helianthus annuusTreat malaria, treat bacterial infections, and migrainesChadwick et al. (2013)
DiterpenesC20Euphorbia, salvia miltiorrhizaAnti-inflammatory, cardiovascular diseasesVasas and Hohmann (2014), Zhang et al. (2012)
TriterpenesC30Centella asiaticaWound healing, increases circulationJames and Dubery (2009)

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Therapeutic effects include:

  • Mucolytic and decongestant
  • Analgesic – pain relieving action is seen in the like of para-cymene
  • Antiseptic – as seen in lemon, rosemary, and pine essential oils
  • Stimulant – as seen in rosemary
  • Tonic – as seen in bergamot
  • Antiviral – as seen in lemon which is used for warts, herpes and colds
  • Anticarcinogenic – fights cancerous cellular activity (source)

We use oils high in monoterpenes to address respiratory tract infections, pain, infections, chronic fatigue, exhaustion, convalescence, depression and poor mental clarity. Oils high in monoterpenes include Angelica root, the citrus oils, elemi, juniper, fir, balsam, somalian frankincense, pine, bergamot and rosemary.

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Therapeutic effects include:

  • Anti-inflammatory – as seen in german chamomile and ginger
  • Antiseptic and antibacterial – as seen in myrrh
  • Calming and hypotensive
  • Analgesic
  • Anti-spasmodic

We use oils high in sesquiterpenes for addressing inflammation, allergies, infections, pain, anxiety, depression, insomnia, tension (muscular and nervous) and spasmodic conditions of the digestive system. Oils high in sesquiterpenes include ginger, myrrh, german chamomile, virginian cedarwood.

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Therapeutic effects include:

  • Analgesic – consider menthol in peppermint
  • Sedative – as seen in linalool
  • Anti-microbial
  • Antispasmodic – as seen in basil, sweet marjoram and peppermint
  • Vasoconstrictive – may contribute to analgesic action that is demonstrated by the likes of menthol and geraniol (which makes our skin feel cold when applied)

We use herbs high in monoterpenols to address pain, stress, anxiety, depression, tension (muscular and nervous), spasmodic conditions of the digestive system, and infections. Oils high in monoterpenols include tea tree, basil, pamarosa, rosewood, eucalyptus, citronella, juniper, geranium, sweet marjoram, peppermint, rose, neroli and lavendin.

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Therapeutic actions include:

  • Anti-inflammatory – seen by alpha-bisabolol found in the chamomile oils
  • Anti-viral

Used to address inflammation, allergies and viral infections. Oils high in sesquiterpenols include Vetiver, sandalwood, patchouli and virginia cedarwood.

Sandalwood (source) – Check out how to grow sandalwood in your garden!

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Therapeutic effects include:

  • Antimicrobial and immunostimulant – such an important action of the phenols and is highlighted by the renowned antiseptic nature of thyme essential oil.
  • Rubefacient
  • Tonic and stimulant – as seen very well in oregano essential oil. 

Addresses musculoskeletal pain and inflammation, infections, exhaustion and convalescence. Oils high in phenols include thyme, oregano, clove bud, cinnamon leaf, bay and summer savory. 

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Therapeutic effects include:

  • Calming and sedative – citral and citronella (found in lemon balm)
  • Antimicrobial
  • Hypotensive
  • Vasodilator
  • Anti-inflammatory

Addresses: stress, anxiety, depression, tension, nervous tension infections and inflammation. Oils high in aldehydes include: cinnamon bark, may chang, lemon balm, citronella, lemon, lemongrass

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Therapeutic effects include:

  • Cicatrisant
  • Mucolytic and decongestant
  • Anti-viral – consider oils such as rosemary
  • Analgesic – frankincense is a prime example

Oils address: respiratory infections and allergies, common coughs, colds and other viral infections and pain. Oils high in ketones include: hyssop, spearmint, rosemary, yarrow, turmeric, frankincense

Turmeric plant (Source) – Check out how to grow your own turmeric at home!

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Therapeutic effects include:

  • Antispasmodic
  • Sedative – acting, it’s thought, through regulation of the sympathetic nervous system and via the neuro-endocrine system. Linalyl acetate is an interesting example of an ester with sedating actions (esters are present in many sedating essential oils)
  • Anti-inflammatory
  • Analgesic
  • Antifungal

Addresses: stress, anxiety, depression, nervous tension, muscular tension, inflammation, spasm in the digestive tract, pain, and fungal infections (athlete’s foot and fungal nail infections) Oils that are high in esters: wintergreen, clary sage, petitgrain, lavandin, roman chamomile, lavender, myrtle, ylang ylang, jasmine, geranium and palma rosa.

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Using essential oils

We might use several methods of applications or preparations of essential oils so we feel compounding effects in our treatment plans. Here are a few of them and how they work.

Different essential oil application methods (source)

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Vaporizers and diffusers are a very easy way to send the volatile molecules in an essential oil up into the air. Our brains are immediately stimulated (via our olfactory bulb) whilst these volatile molecules move around us. For use in a vaporizer or diffuser a herbalist might choose calming, relaxing or even sedative essential oils to ‘sit’ in the air in the environment of those suffering from stress and anxiety. 

Oils to consider for promoting calm include: lavender, sweet marjoram, vetiver, roman chamomile, petitgrain, mandarin, lemon, orange, neroli, jasmine, rose, frankincense and ylang ylang. If we want to improve mental clarity and help clear brain fog, we might consider basil, peppermint, eucalyptus, rosemary, clary sage or juniper berry (juniper is particularly good for those who will be working with and communicating with lots of people).

Throughout history, we’ve been purifying the air with antiseptic essential oils. Vaporisers and diffusers using antiseptic oils can be considered by us when they’re working on supporting a client’s immune system. Useful antiseptics: lemon, thyme, eucalyptus, cajeput, niaouli, clove, cinnamon, pine, lavender, german chamomile, sandalwood and peppermint.

*Caution: some diffusers are dangerous for pet health, so do diligent research if you have fur family.

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Dry Evaporations

Placing drops of essential oil (or a blend) onto a tissue lets us experience “dry evaporation”. This can be a key strategy for the management of nausea and vomiting when other applications might be impractical or too much for someone feeling very unwell. A pregnant mother struggling with her hypersensitive sense of smell and her terrible nausea needs just 1 drop of an antiemetic essential oil to bring relief. These herbs are: peppermint, ginger, spearmint, 

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Steam Inhalations

Steam Inhalation – note the closed eyes (Source)

Great care must be taken when applying a steam treatment. Occasions where steam treatment is not recommended include those with severe asthma, those with very sensitive skin, those with movement disorders that could knock over the bowl of hot water. For respiratory issues such as the often painful sinusitis, concession and catarrh resulting from coughs, colds or the flu, for tonsillitis, bronchitis or earache, the deep, moist inhalation of steam laden with essential oils will allow for deep, rapid penetration of these therapeutic molecules into the respiratory system, reaching the sinuses and middle ear. The oils will be able to reduce inflammation, soothe hot and irritated mucous membranes, loosen and dislodge excess mucus and catarrh, and exert an antimicrobial effect. 

To carry out a steam inhalation we need a suitably sized bowl. Fill the bowl with water hot enough to produce a decent steam. Steam inhalations produce a rapid and powerful essential oil treatment and we need far less essential oil. Add no more than 3 drops of oil per steam. Place the bowl on a sturdy structure and seat the client by the bowl. Drape a towel over their head as they bring it down over the bowl. They must keep their eyes closed as soon as they start moving towards the bowl and an eye mask adds a second level of protection for the highly sensitive eye. If treating a child – having carefully assessed the risks outlined above – use only 1-2 drops of essential oil. This same lower dose is advisable for pregnant women and the elderly or constitutionally weak. Ask the recipient to start with slow breaths, through the nose and not too deep. After a few slow nasal breaths, the recipient can try some inhalations through the mouth. If all is well, they can alternate between nasal and mouth breaths.  

Herb oils used in steam for upper respiratory infections: eucalyptus, niaouli, rosemary, thyme, and ravensara, and also tea tree, cajeput, lavender, peppermint, sweet marjoram, basil, german chamomile, sandalwood, lemon, spike lavender, cedarwoods, pine, hyssop, fennel, clary sage, frankincense and myrtle might be of interest when choosing oils. Other symptoms that respond well to steam – dry throats, congestion, tickly dry coughs, sore throats. Therefore, steam might go well alongside a soothing cough syrup or herbal infusion.

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Showering and Bathing

Therapeutic baths are extremely rejuvenating (source)

Bathing as a method of application is wise when looking to use oils daily to address long standing stress and anxiety issues, or for those living with depression. Baths are also great for those with regular headaches and migraine and to help manage insomnia alongside relaxing, sedative herbal remedies. 

For skin conditions, either long-term or acute, the longer exposure time of oils in a bath should be weighed up and the oil choices carefully considered, to make sure that the heat of the water and the prolonged exposure aren’t going to irritate the skin. Used correctly, a daily bath with the right oils for the skin issue can be a powerful addition to herbal treatment. Remember though, skin conditions respond best to water-based herbal preparations internally. 

Adding essential oil to the bath is great for musculoskeletal disorders, which will certainly benefit from a daily application of essential oils and warmth. Consider this for those with menstrual cramps, starting the baths a few days before the usual initiation of the pain. 

When adding essential oils to the bath, they need to be added with a fat (e.g. a carrier oil or milk) that will help disperse the oils and prevent them from floating atop the water, where they could irritate the sin as they’d be undiluted. Be aware that some oils are more likely to irritate when used in this medium, notably the citrus oils, peppermint, and the spices. No more than 8 drops are necessary in a full bath, diluted down with fat.

Hand and foot baths are another good choice to manage conditions such as arthritis, sprains and strains, circulatory issues, varicose veins and more. We many wish to consider footbaths during infections where they can be used in fever management and to promote feelings of comfort and well-being, especially in the very debilitated. Children and the elderly respond particularly well to foot baths. We need only 3-4 drops of oil, diluted down in a fat. 

For some, a daily bath isn’t practical, and therefore a product to use in the shower might be better suited. Base shower gels can be blended with essential oils and whilst the product is washed away quickly, the aromatic benefits will be there, and warm skin does absorb oils rapidly. Another way to use oils in the shower is to rub a diluted blend of oils (e.g. essential diluted in the carrier) into the skin at the end of the shower. Either leave the oil on and exit the shower, or wait for 30 seconds (all the time needed for the oil to absorb) and continue the shower. Those going to bed or work might prefer to option to rinse off the remaining carrier oil. You could also hang a bundle of herbs from the shower head and let the hot steam activate the active constituents in the herbs, essentially making a steam inhalation shower. Shower applications are especially useful for menstrual cramps, circulatory issues and musculoskeletal complaints. 

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Follow-up post :

Essential Oil Starter Kit – 26 herbal oils every home must have

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