Essential Oil Basics (for Animals & People)

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I’ve wanted to record an episode on essential oils for a long time now, but there is SO much information out there and I wanted to do this topic justice. After much deliberation, I’ve decided to pull the information for this episode almost exclusively from a reference book that I purchased a few months ago and use frequently, The Animal Desk Reference by Dr Melissa Shelton.

This is for a few reasons, the first of which being this book is 585 pages long and has a TON of references so I do trust the information in its pages. Second, there is a ridiculous amount of information about essential oils on the internet and I didn’t want this episode to be 6 hours long.

So today I’m going to go over what essential oils are, how they are absorbed into the body, methods of administration, proper dilution, possible drug interactions, and finally how to choose a high-quality oil.

What are Essential Oils

Essential oils are “the aromatic and volatile chemicals contained within certain aromatic plant species” (1 – pg 19).

  • I find that the word “volatile” can be intimidating when people hear it but in the context of essential oils it simply means “an oil that vaporizes readily” (2)

Not all plants have a volatile oil component (and thus cannot be turned into an essential oil).

“Essential oils are considered a secondary metabolite to the plant” (1- pg 19). This means that while they are “not directly involved in the normal growth, development, or reproduction of the organism”, secondary metabolites “aid a plant in important functions such as protection, competition, and species interactions” (3).

These essential oil compounds are then stored in various parts of the plant, this location varies in each plant. This is why every plant has different requirements for harvesting techniques and distillation methods. Some plants can even create different essential oils based on what part of the plant is used. For example, “clove can be from the bud or from the leaf. Cinnamon can be from the bark or the leaf. Even though from the same plant, the essential oil can be quite different.” (1 – pg 20)

I’m not going to lie, I was not a huge fan of Chemistry in high school or university, in fact, it was probably my least favourite class (after Stats because at least you could blow things up in chem occasionally). To really get into the science of essential oils requires a little more chemistry than I would like, and frankly would probably not make for a very entertaining episode for most people.

  • All of that to say, there are 9 functional groups that can be combined with varying hydrocarbon bases to make up the essential oils.
  • The main functional group you will likely hear mentioned is “phenols” as this is the root of most people’s concerns with using essential oils around cats. I’m planning to do a whole episode on essential oil use and cats in the future, but for now, I’ll quote Dr Shelton directly in saying that “much of the information is based on very old research, with very little attention to current and updated veterinary knowledge… When used properly, phenols can be an important part of veterinary aromatic medicine” (1- pg 27).
  • To learn more about essential oil use with cats I highly recommend reading this article.

Again, if you are interested in learning more about the chemistry side of this, I would recommend using the almighty power of the internet.

Absorption of Essential Oils in the Body

Absorption “can occur through many methods. Through the dermis or skin, through the buccal or mucous membranes, through the gastrointestinal (GI) tract, orally, through the lungs via inhalation” (1 – pg 62) just to name a few. The amount of absorption that occurs may vary greatly depending on the way the oil is administered, the dose given, and the frequency of the dosing. Absorption also varies based on the type of essential oil being used, certain oils are more easily absorbed via inhalation, while others are better absorbed dermally.

The species of animal (and possibly even the breed) will also affect absorption, Dr Shelton notes that “hair follicle density in animals may play an important role in how much essential oil they absorb” (1 – pg 62). This is because hair follicles secrete an oily substance called sebum on to our skin, essential oils are fat soluble (lipophilic) and thus will absorb more readily into the skin of animals with more hair follicles. Dr Shelton notes that this is why Chinchillas -with the highest fur density of any land mammal- are more sensitive to essential oil absorption than animals like dogs, cats, or horses. So if you have an animal that is extremely furry, use caution when administering oils topically.

So now that we’ve covered absorption in general, let’s talk about ways to administer EOs…


First let’s talk about the most common method of absorption, inhalation.

Inhalation can be from smelling the oil directly from the bottle, diffusing it via a gadget of some sort (eg an ultrasonic diffuser), or via diffuser jewelry or collar attachments. Dr Shelton says the following about inhalation “it is incredibly safe when high-quality essential oils are used, and incredibly easy as we do not even have to touch the animal to administer”  (1- pg 64).

She goes on to discuss how when the lung excretes the essential oils it was exposed to, it forms what she calls “therapeutic mucus”. She explains this process much more clearly than I could, saying, “the essential oil is inhaled into the lungs. Some of it is absorbed into the bloodstream, some is metabolized in different areas of the body including the lung, and most is likely exhaled or excreted at the lung location. Just like with a dust particle, when it is inhaled, it is trapped in mucus, and tiny little cilia (hairs) on the cells lining the respiratory tract move the particle up and out of the lungs and airways… the glory of this conveyor belt [is that] it is exposing the surface of the respiratory tract to the essential oils AGAIN” (1 – pg 65).

Topical Use (aka Dermal Absorption)

Anytime an essential oil comes in contact with the skin, even via creams, mists, shampoos, or diffusion it is considered dermal administration. Sometimes, the hope with dermal administration is to treat a localized area, possibly to reduce swelling or speed healing in a targeted location. But oils applied topically can also have a total systemic effect, an example Dr Shelton gives is oils dripped on the back with the goal of supporting the liver need not be applied directly to the liver location.

Topical applications avoid first-pass metabolism and also have the added benefit of the “aromatherapy” effect in that the animal can also smell the oils being used and inhale them. This can also be a downside of topical use, however, as some animals may not like the smell of the oils. Oils used topically also have the potential to irritate the skin and so we must dilute accordingly and use caution with this method.


As oils are lipophilic (aka fat soluble) we typically dilute using a high-quality carrier oil.
The best option in my opinion (and Dr Shelton’s coincidently) is fractionated coconut oil (coconut oil that stays liquid at room temp and does not stain fabrics).
Dr Shelton has a whole chapter dedicated to dilution but to summarize quickly the ideal dilution concentrations are

  • 3-7% for cats
  • 5-50% for dogs
  • 10-50% for horses

This means that when you need a 5% concentration, 5% of the mixture would constitute the essential oil, and the other 95% would be a carrier substance. This gets into math a bit more than I’d like but you should be able to find the right values for set amounts of oil by doing some googling.

This is typically how I figure out my solution ratios:

  • Find out how many mL are in my desired container
  • Figure out what concentration I want my mixture to be
  • Google how many drops I need to add


Ingesting Essential Oils

Ingesting EOs subjects them to “first pass metabolism”, meaning the oil is exposed to metabolism in the liver before reaching a specific/intended bodily destination. According to Dr Shelton, first pass metabolism decreases the bioavailability of the oil and will lower its therapeutic effects. However, taking and sublingually (under the tongue) or buccally (absorbed between gum and cheeks) will bypass the first metabolism and result in a more oil being left available for use in the body.

She also notes that although we do see benefits with these methods, we should “strive for the use of other routes if they are effective”. She goes on to say that it has become “a bit of a popular misconception” that oral administration is necessary or superior and that it in her opinion it is best to “use the easiest and least problematic route of administration for each animal until it shows that it is not effective enough. Basically, do not jump right to oral administration when topical application may do” (1 – pg 69). Other downsides to oral administration include potential GI upset and food aversion.

Possible Drug Interactions

My standard disclaimer applies here: always consult your veterinarian concerning the medical needs of your pet (in terms of oil interactions I would recommend trying to find a vet who is well versed in oils, likely a holistic/integrative vet). I also recommend doing ample research via books like The Animal Desk Reference.

Certain oils, when used improperly, can have negative interactions with the medications your pet may be taking. They can alter the speed at which the drug may be metabolized and can also increase or decrease its effectiveness. One example Dr Shelton notes is the effect of wintergreen on anticoagulants.

Choosing High-Quality Oils

This is a bit of a hot topic on the oil-loving community and many people are very passionate about which oils companies are “best”. So before we jump into this too far I want to say that in mentioning a particular brand I am by no means implying that other brands are inferior or sub-par.

However, it is true that there are definitely sub-par brands on the market (I’m looking at you cheap amazon & grocery store options) but there are also lots of great brands out there as well. There is very little regulation in the essential oil market and labels and grading can be deceiving. I’m a big fan of Dr Shelton’s advice on using organoleptics. Meaning, we assess each oil via our senses of sight, touch, smell, and taste. You may like one oil from one brand and yet another oil from another brand.

Click here for the oils I use & love. 

Personally, I use mainly Young Living Oils as I have had great experiences with them, however, this may change in the future if a new brand comes along. Dr Shelton also has her own line of single essential oils & blends that are specialized for animal use, called AnimalEO.



  1. The Animal Desk Reference by Dr Melissa Shelton 


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