Essential Oils — Beyond the Pleasing Aromas

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Essential Oils — More than Just A Pleasing Aroma

Essential Oils are fabulous. We all love them for their amazing power to uplift, calm, delight, and fascinate our spirits. We blend them together to get a unique scent profile for ourselves, and even for our pets! I love using our Pet EO Blend of Cypress, Cedarwood, Citronella, Lemongrass, Lavender, and Tea Tree in shampoos and bedding sprays. Sometimes a single note is exactly what we want — like Lavender, Rose, or Jasmine. But as great as EOs are for creating aromatherapy combinations and beautiful scent profiles, there’s a lot more behind an EO that many of us don’t realize.  So today we’re going to talk a little about the chemistry behind EOs.

Essential Oil Chemistry 101

As someone who successfully avoided Chemistry throughout high school and in college, imagine how surprised I was to be confronted with the subject as an adult formally studying Aromatherapy! Though it was difficult, studying the chemistry of Essential Oils provided me with an in-depth understanding of their complex chemical compositions and their proper usage.  I also learned that it would be nearly impossible to create an Essential Oil in a lab, as each and every chemical constituent that we know and love is already included by nature.

What gives an Essential Oil its Properties?

Each EO has unique multiple chemical properties that influence the aroma they give off.  When you can break down an Essential Oil into to its distinct properties, you can begin to understand how that Oil gets its scent and how the different constituents work together. Essential Oils consist of hundreds (sometimes thousands) of chemical constituents, also known as Organic molecules and chemical compounds or “building blocks” that include hydrogen, oxygen, and carbon. Each of the Oil’s properties works in tandem with the other to rebalance a variety of conditions.

In general, Essential Oils fall into two distinct groups of chemical constituents; the hydrocarbons, which are made up almost exclusively of terpenes (monoterpenes, sesquiterpenes, and diterpenes), and the oxygenated compounds which are mainly esters, aldehydes, ketones, alcohols, phenols, and oxides.

Below is an abbreviated list of the constituents in an Essential Oil, beginning with Terpenes, which are evident in nearly all Essential Oils.

Hydrocarbons (Terpenes)

Terpenes (/ˈtɜːrpn/) are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers and as well, Cannabis sativa plants. Comprised of Hydrocarbons, Terpenes found in most of the Oils and include Monoterpenes and Sesquiterpenes. I have always referred to Monoterpenes as the ‘sunny’ constituents.  Monoterpenes provide a warming or “sunshine” sensation to the skin and call to mind aromas of Citrus.  Pinene and Limonene are the two most common of all of the constituents that make up Essential Oils.

Oils containing Monoterpenes include:

  • Limonene- found in Bergamot, Carrot, Fennel, Lemon, Neroli , Orange and other Citrus Oils
  • Pinene- found in Coriander, Cypress, Eucalyptus, Pine, Black Pepper, Oregano
  • Camphene-found in Juniper, Fir, Spruce, and Pine

Next, we have Sesquiterpenes: I refer to Sesquiterpenes as the ‘calming and soothing’ constituents. When I smell oils with a high percentage of Sesquiterpene, I feel immediate relaxation. I always carry a dram of Clary Sage Essential Oil with me; it’s my go-to EO for helping me relax after a stressful day.

Oils containing Sesquiterpenes include:

  • Carophyllene- found in Lavender, Clary Sage, Marjoram
  • Azulene & Chamazulene- found in Chamomile
  • Cadinene- in Patchouli, Lemon, Cedarwood

Oxygenated Compounds

Oxygenated Compounds mainly include Aldehydes, Phenols, Alcohols, and Esters.

  • Aldehydes– When I smell oils with a considerable amount of Aldehydes I think of Citronella candles burning on a Spring evening– hopefully providing an aroma that will give bugs something interesting to think about rather than sharing their venom! Not all Aldehydes provide this fruity aroma, however. Aldehydes are actually one of the compounds that drive the scent of an Essential oil and include:
    Cinnamaldehyde Acid – prevalent in Cinnamon Bark Oil, also in Patchouli
    Anisaldehyde- prevalent in Anise Oil
    Benzaldehyde- in Bitter Almond Oil
    Citronellal-in Lemongrass, Lemon Balm (aka Melissa)
    Citral- Bergamot, Lemongrass, Cistus
    Geranial- Lemon, Lemongrass, Cistus and Lemon Balm
  • Phenols– I tend to think of a Medicinal/Herbal aroma when I think of oils that are high in Phenols. Two kinds of Phenols exist in Essential Oils- one is naturally occurring and the other occurs in the distillation process.
  • Eugenol– is very prevalent in Clove oil. (You might recall the scent of Clove when undergoing a dental procedure). Other oils that contain Eugenol are Bay, Basil, Cinnamon, Rose, Ylang Ylang
  • Thymol– in Thyme Oil, Sage Oil
  • Methyl Chavicol– in Basil Oil, Fennel, Hyssop, Marjoram, Anise
  • Anthethole- Fennel
  • Carvacrol-in Black Pepper, Marjoram, Thyme, Fennel
  • Alcohols-A very large functional group of constituents which are categorized as “Monoterpenic”, “Sesquiterpenic” and “Di-Terpenic”, the latter in small amounts and the first mentioned the most common.
    Geraniol- in Bergamot, Geranium, Melissa, Neroli, Grapefruit
    Menthol- -in Lavender, Peppermint
    Linalool- in Basil, Bergamot, Clary Sage, Lavender, Marjoram, Neroli, Thyme, Ylang Ylang, Coriander, Ginger, Oregano
    Borneol- in Juniper, Frankincense, Lavandin, Hyssop
  • Esters – Essential Oils that contain Esters are quite fragrant with a fruity type of Aroma to my nose. When I smell oils with a high Ester Content I feel automatically relaxed, perhaps it is due to the intense aromas of these organic compounds or more so because I simply love ester-heavy oils.
    • Linalyl Acetate- in Lavender, Bergamot, Clary Sage, Geranium, Lavandin, Jasmine, Petitgrain
    • Benzyl benzoate- Benzoin, Jasmine, Ylang Ylang, Balsam Peru
    • Geranyl acetate- in palmarosa, lemon grass, petit grain, neroli, geranium, coriander, carrot
    • Borneol Acetate- in Yarrow, Rosemary, Pine, Juniper

When thinking about creating your own Essential Oil blends, I hope this gives you a little insight into the WHY behind the fabulous aromas you envision.

Happy Creating,


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5 years ago

Hey Kathy!
Do you have any interest in being a member of the Oregon Lavender Association? The association consists of about 75 members, about 1/3 of which are lavender enthusiasts, 1/3 are in lavender-related businesses (products, distillation equipment, etc.) and 1/3 are lavender growing visitor destinations. We have quarterly educational meetings and newsletters. You might find it of benefit to you and/or Essential Wholesale. We’d love to have you join us! Learn more at

5 years ago

Hi Bonnie, I’ll pass your kind invitation along to Kathy. Thanks for reading!

5 years ago

This is way cool. Thank you!
I have a question about Melissa. I love the fragrance yet it’s really hard to find . Do you carry it in your line of oils??

I barely passed chemistry in high school. Wish I had s teacher like you !

5 years ago
Reply to  Brenda

Hi Brenda, we don’t carry Melissa. Also known as Lemon Balm, it has a super beautiful scent. But it’s also super expensive, which is why it’s so hard to find. I do know people grow it in their gardens, so that might be an option. I’ve never grown it, but if it is like other mint-family plants, you might want to grow it in a container.

5 years ago

Kathy, I’m working on my level 2 certification, I love how you explained this so well and easy to understand this will be so helpful. Thanks

5 years ago

Hi kathy

How do you get into the studies of aromatherapy? Oils ,hebals, and plants. Do you have any recommendations for how i can study these things .

Penny Crooks
5 years ago
Reply to  Melanie

There are Aromatherapy schools available for learning across the US and some of them have long distance learning which is what I am doing. Aroma Head Institute, Aroma Apothecary Healing Arts Academy, and many others. Search it on the web. I’m finishing up my level one and will be going into level two soon. Also there is the Aromatherapy Trade Council, International Federation of Aromatherapists, Aromatic Plant Project and other good organizations. Good Luck !

5 years ago
Reply to  Melanie

Kathy took classes from a woman here in Portland. There are great books out there and I’ll get a recommendation or two from Kathy.

5 years ago
Reply to  Val Sanford

Here are Kathy’s recommendations for books:

Jeanne Rose: 375 Essential Oils and Hydrosols
Patricia Davis: An A-Z Aromatherapy
Julia Lawless: The Encyclopedia of Essential Oils

There are scores more but these are my favorite go –tos.

Diana Nutt
5 years ago

Hello Kathy!

Wondering if you have any suggestions for some kind of fragrance oil that would pair well with a soap that is made with iodine and kelp. A friend of mine who is a hot process soap maker novice…(whew!) created a “medicinal” soap that is…to put it politely, rather earthy smelling. It needs help. The smell is not user friendly. I was thinking maybe be fir pine or eucalyptus to help blend with it. Thank you so much.

5 years ago
Reply to  Diana Nutt

Hi Diana, I asked Kathy your question and here’s here answer.

Wow, that is quite a combination!!

Perhaps using some heavy duty base notes will work- Patchouli, Oakmoss, Vetiver might do it. I also do like the idea of trying the coniferous oils, it is just one of those situations where one needs to try it and see if it works. Eucalyptus also sounds like a god idea- Rosemary might be a good one in this case too.

But I supply this suggestion based upon masking nasty scents for Cold Process Soap- lye soap, I want to be sure we are speaking of the same process, it may or may not make a difference, I am only familiar with Cold Process.

Again best to know this is for lye soap- I hope this offers so help- let me know if not and we will try another avenue.

5 years ago

I will be starting a Essential Oil blending bar for natural body products and healing blends that I can dilute in carrier oil for applying, Questions in your Essential oil blends what would you suggest in the collection for healing aromatherapy?
thank you

3 years ago

Hello there,

Hoping someone can help me out with my inquiry! I recently have become obsessed with my diffusers and relaxing essential oils- I really love how relaxed they can make you feel and help to sleep. I unfortunately have just learned that certain essential oils are actually TOXIC to cats…. I have a cat and as you can imagine I’m quite concerned for my “fur baby”!!! I’ve been reading many sources online that are giving conflicting responses as one will say a certain oil is bad and another will say that same oil is ok. I guess it comes down to the chemistry of the cats liver, unlike a dog, lacks a certain enzyme to breakdown and detoxify certain oils which actually ends up causes liver failure and fatality. As you can imagine this really upset me. I don’t want to stop using essential oils in my diffuser but I am concerned for my cats health and well being. I was told by someone that they had spoken with their vet and was told not to use any oils high in Phenols as these are the toxic ones. You can find a list online which only contains about 7-8 oils. I am not 100% satisfied with this because no citrus oils are included in the list and neither is eucalyptus or lavender yet I have read from other sources those are toxic as well… again then some sources say citrus, lavender and eucalyptus are good for cats! You can see how confusing this has all become for me. I’m hoping someone on her is educated on this matter and is able to assist me further with educational facts rather than random people writing things on google about this topic.

3 years ago
Reply to  Sharon

Did anyone ever answer you regarding the cats and which ones are harmful to them. I had the same question and no one seems to want to answer the questions there’s so much conflicting stuff on the web and I really want to protect my feline fur babies.

Bon Quaintance
2 years ago

Sharon, I noticed this old post:

Both cats and dogs have extremely sensitive senses of smell. Using diffusers of any type, especially fountains which a cat may mistake for a water source, yikes, may add too many molecules into the air. Using bamboo sticks soaked in olive oil with 10-20+ drops of YOUR scent of choice (depending on the strength of the oil), is safe as a rule. Nix the incense. It’s not in their best interests and can, in some cases cause bronchial or or other ailments. We don’t want that!

Valerian is a known cat favorite although my Abysinnian didn’t like any scent except a small amount of Thyme. Go figure. My Bengal went berserk for both Valerian and Cat Mint. Catnip is at the top of the Cat Mint pole, but I would recommend not using oils for your pets in diffusers, just rub some on a cloth, on their scratch post or, if they have access to the outside for short periods, setting aside a space for a cat garden would be Nirvana for your furry children and they will love you for it!

Most plants in the genus Nepeta cataria (such as catnip), are cat faves and have beautiful flowers as well.

Ana Malachevsky
1 year ago

Hi Kathy,
Is it known if the citrus essential oils produce allergies in some people?
Thanks, Ana

1 year ago

Hi Ana,

According to one of our formulators, essential Oils are extremely concentrated, so it’s possible that people could develop allergies to any essential oil. This is one of the reasons to never apply an essential oil to the skin without diluting first into a carrier oil.
There are some that have proven to be less likely to cause allergies such as lavender, however, anyone can develop an allergy at any time.