This blog post is somewhat a continuation of the previous blog that Marija Kolarović, Mr. Ph. wrote for us. This was one of our most popular themes in the online courses we provide and so we decided to share it with everyone. Please, make sure to read the previous post for the introduction as well as watch the video explaining this in practice.
The original question from our readers:
I would you to explain the fact that when making blends, two oils with a component such as alpha-terpineol considering their individual percentages, when mixed together take a different percentage in that same component and not their sum. For example, looking separately Cypress has 0.30% alpha-terpineol and Rosemary 1.30%. In the mixture of 3 drops of Rosemary and 2 drops of Cypress, the alpha-terpineol content in Dropsmith appears to be 0.90%.
Does this happens always and with all the essential oils?
If so, the formulations that I have made so far may not reliable because if, for example, I want an make an antifungal blend and I focus on the geraniol component, I could choose Palmarosa and Geranium as the highest in that component. But when I mix them, they will not be as powerful in geraniol as single Palmarosa EO. Therefore, it will not be as powerful as I believed. So then, it is preferable not to mix and stay with the essential oil with a higher percentage of geraniol?
(My) Melani’s answer:
In my many years of teaching, I’ve noticed that is a common misunderstanding in the aromatherapy world and that is why I’ve encouraged Marija to mention it but because it can be tricky to understand I’ve also made a video (right below Marija’s text) to explain further. I was very excited to get this response because that tells us that we’ve touched on a topic that needs to be addressed more. So I’ve explained the questions in the video below, making it a bit more visual, and then my colleague Dr. Petra Ratajc will go into more detail below.
I hope you’ve enjoyed the video:)
Also, I’ve added the picture from the video for your reference.
Percentage of a specific constituent in an essential oil is expressed as a part of the whole essential oil, and the sum of concentrations of all constituents gives us 100%. When we blend essential oils, the contents of individual constituents of each essential oil sum up, however, the volumes (or weights) also sum up, which we need to consider when we calculate the final concentration of constituents. As the total volume (or weight) of a blend will always be bigger, the contributions of each oil will average out according to their weight in the blend.
So if we mix equal amounts of oils with 80% and 90% of some constituent, the blend will contain 85%, and if we mix 10% and 90% solution, the blend will be 50%.
Let’s look at some simple calculations with different ratios.
We want to blend two EOs (EO1 and EO2) with 40% and 60% of constituent X. What will be the final concentration of the constituent X?
- For 1:1 ratio, we blend 1 part of EO1 and 1 part of EO2, and get 2 parts of the blend. For the final concentration of the desired constituent, we need to divide the sum of concentration by 2!
- For 1:2 ratio, we blend 1 part of EO1 and 2 parts of EO2, and get 3 parts; therefore the sum of concentrations needs to be divided by 3.
For detailed calculations, please see the picture below:
Petra is a biologist, researcher and educator. She received her PhD from the University of Ljubljana, evaluating quality of local medicinal plants and their essential oils. Her primary interests are medicinal and aromatic plants and secondary plant metabolites, with the main focus on safety, efficacy and pharmacology of essential oils and other herbal products. For the last few years, Petra has been engaged as a lecturer and expert book reviewer and is the author of the research about the home use of essential oils in Slovenia. She regularly cooperates with Slovenian and international herbalists and aromatherapists. In 2017, Petra started an international blog The PhytoVolatilome, with the aim to present plants and essential oils in a wider context, share independent information and empower readers to make informed decisions.