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Essential Oil Encapsulation and what it can do for you.

January 20, 2020

In my job as a cosmetic formulator, I mostly get involved with essential oils when a client wants to fragrance their product naturally and prefers the idea of an essential oil based aroma over something synthetic.  That said, there are also many clients who see essential oils as part of their range of actives and a few are tempted to use them as preservatives although that often doesn’t work out too well. Suffice to say that essential oils often make up part of the formulations that I create and develop.

Using essential oils as your fragrance is a great way to turn what would otherwise just be a ‘perception’ ingredient into a ‘reality’ ingredient in as much as a synthetic fragrance just make things feel good whereas essential oils can actually do some good too.  However, it’s not quite that simple, essential oils often contain natural weak spots – chemistry within their mix that is challenged by the formula environment.  Over time the essential oils in a formula can oxidise or chemically change, in some cases causing the product to discolour and in others causing the product to become more irritating to the skin.  On top of that, some essential oils can be quite corrosive to packaging,  especially when used at higher amounts or when added into a sub-optimal formula (where the essential oil isn’t fully solubilised or integrated).  In these cases packaging failure can accelerate oxidation or negatively impact the publics perception of the product due to pump failures, packaging cracking or discolouration or a dissolving of glue and weakening of packaging glue.  The above are all examples of what we look out for during stability testing as some of these changes are only measurable or perceivable over a period of time.  Stability testing typically puts the product under heat stress for a set period of time, 3 months at 40C gives us insight into what might happen at room temperature over 12 months.  Twelve months of really good stability is quite often the minimum standard one should aim for in a commercially viable product and that is no way a given if your product contains unprotected essential oils.

Protection of essential oils in a product comes in many forms and a formulator will consider all of these things in the R&D stage.  The use of appropriate antioxidants to reduce and/or slow down oxidative chemical changes (over the nominated shelf life) is a common step.  Most people who put recipes and formulations together will have noticed there is nearly always a ‘vitamin E’ step these days.  In the old days (so to speak) this may well have been a BHT/ BHA step but now, with the push for vegetable derived solutions it’s mostly tocopherols that do the holding back of oxidation.  Tocopherol (vitamin E) in its mixed state (Alpha, Beta, Gamma, Delta Isomers) is a pretty good formulation partner in this regard being relatively cost effective, long-lasting (much more stable than BHT/ BHA), readily available and easy to incorporate.  However, it’s not perfect, has a slight to sometimes quite strong odour of its own and an oil solubility that is logical and necessary for its function but makes it hard to combine into a spritz spray formula due to its effect on the dispersed phase solubility.  Other options are available to compliment or replace vitamin E including Rosemary Antioxidant (Amiox from Alban Muller is popular) and then Ferulic Acid,  Hydroxyacetophenone, Vitamin C (although this is often the first thing to oxidise as it’s very unstable compared to vitamin E), Coenzyme Q10, plant polyphenols, Alpha Lipoic Acid and many more besides some of which will be present in your plant based actives and others you may add specifically.

When it comes to antioxidant selection (for product protection) I always go along with the ‘eat a rainbow’ mentality. What I mean by that is, a combination (eating the rainbow) is more nutritious (or stabilising) than just sticking to one colour (say just eating broccoli).  The reason for this is that there are many reactions that go on in a formula that may speed up oxidation and so using a few different tools will give you a few more chances to mop everything up before it overruns your formula.  Indeed, on a simple level this is why mixed tocopherol generally out-performs alpha tocopherol alone in product protection – because it is one ingredient with four ‘faces’, each of which performs slightly differently thus giving a broader antioxidant coverage than just the alpha alone.

As good as loading up a formula with antioxidants is, it isn’t always the answer to your formulating problems, especially when you wish to achieve a very long shelf life (in excess of 24 months maybe) and/or have a very natural or very naturally active formula.   One other strategy that has been around for some time is encapsulation technology, this is where the active part of the formula is protected from oxidation and other environmental stressors by wrapping it up in a shell.  This technology has been successfully used to protect volatile chemical mixtures such as essential oils and other flavour and fragrance combinations across food, pharmaceutical and cosmetic industries and again, while it may not be the perfect solution for every formula, it is well worth diving into.


Encapsulation. 

The first time I came across encapsulation in the essential oil space was back in the late 1990’s  when CLR Berlin brought out an encapsulated Tea Tree Oil called Epicutin TT which they may well still sell.  I was working in my first cosmetic job and the ingredient distribution company that I was working for was the agent for this manufacturer so I got to hear quite a bit about their products and technology.  I remember the contents of this article being quite eye opening to me as a young science grad and new industry participant as it was probably the first time when I really saw how scientific the cosmetic industry could be and that excited me!

This table from the above article  stood out to me as it was both simple and complex in the data  it  presented.

This table really brought it home to me that we can think of essential oils as single entities on one level and as complex blends of discrete ‘actives’ on another.  It showed me that there were some ‘actives’ or aroma chemicals within essential oils that were worth a closer look, that some were prone to chemical instability and that we, as scientists could go some way towards reducing this instability if we focus on controlling the ingredients environment.  The fact that doing this wasn’t just good for the (in this case) Tea Tree Oil, that it was also then better for the skin – less irritating, more potent and less smelly – was really quite something. Epicutin TT was developed as an active for blemish prone skin and had sebum reducing properties.

A note on being less smelly.

I mentioned off the bat that my client base often turns to essential oils for their aroma rather than their activity per se, so, it is important to note that the process of encapsulation can and often does change the initial ‘wow’ factor you get from the oil on first whiff.  In the example above, this was actually part of its selling point as not many people swoon over the medicinal odour that is Tea Tree, especially when it’s at the kind of dose needed for a decent result (around 0.5% as active Tea Tree or 5% Epicutin TT as supplied).  So, in this case the lower odour impact of the Tea Tree was a selling point but that isn’t always the case.  Where I have clients who are wanting the perfume of the essential oils rather than the therapeutic benefit per se, encapsulation may negatively impact on that.  So does this make encapsulation pointless for the majority of cosmetic clients?  I don’t think so as what you loose in the volatile, pack-opening WOW factor you gain in the long term in-use experience of the product so it’s probably more of a re-imagining and re-training of how to appreciate the product rather than a case of shunning the technology altogether. I think most cosmetic brand owners would rather the client have a good long-lasting wear presence of the aroma over just a knock-out whiff from the pack, especially given this technology also protects the aroma from causing irritation.

Back to the Tea Tree Example and some application advice.

Out of interest I’ve found and am sharing two promotional formulations that were published to encourage formulators to try the Epicutin TT. I’ve popped the INCI names next to trade names where I could find them  so  you  can  get  a  better  understanding  of  how  these  formulations  look.   One  thing  that  stands  out  to  me  is  how  simple  things were  back  then,  now  it’s  common  to  find  supplier  formulations  loaded  with  so  much  stuff  that  it  would  be  hard  to  know  what  ingredient  was  giving  you  the  benefit…

Encapsulate Technology.

Back then, 21 years ago, the technology for encapsulation of cosmetic actives was Cyclodextrins or cyclic sugar polymers.  There was a pretty decent review article written about this in the Journal of Cosmetic Science back in 2002 and here it is.

As you can see from reading the linked article, cyclodextrin capsules were not new technology in the 1990s, indeed the article found reference to them as far back as 1891 although back then, they were named cellulosins.  In 1903 it was an Australian based microbiologist,  Franz Schardinger, who we can thank for the name cyclodextrin after he discovered that the sugars that form these encapsulates are dextrin based – alpha and beta.  He noted that they form ring structures which explains the logic behind the name cyclo (ring) dextrin (dextrose based sugar).  A fair bit more research went on and by the 1980’s this technology was becoming so interesting that a symposium was held to help further its commercialisation across a number of high-value industries.

As the price of Cyclodextrin technology reduced this chemistry was used to protect all types of active ingredients from the environments they found themselves in.  This included flavour, fragrance, drug and other consumer product applications where active protection and long-term active delivery were advantageous.  The technology was also useful in allowing ingredients that were usually poorly soluble in water to be formulated into watery products thanks to the Trojan horse disguise the inert cyclodextrins provided.

Cyclodextrins can be thought of as protective shells that surround the target active. These shells come in the shape of a donut where the middle (or surface surrounding the donut hole) is oil loving and the outer surface of the donut is water loving.  I was looking around for suitable video to demonstrate this and couldn’t go past this crazy offering from the 1980’s. 

Cyclodextrins are just one example of a physical (and inert in the cosmetic sense) shell encapsulate material, there are many more with each type offering its own features and benefits as well as hold-backs and challenges.  Shells made of Chitosan, alginate,  modified cellulose, tristearin and more besides are available from a multitude of ingredient manufacturers, filled with a multitude of vulnerable materials. This little video gives a very simple overview of why different encapsulating materials may be chosen.   One of the draw backs with earlier cyclodextrin technology was the load capacity of the structure or, to put it another way,  the proportion of the complex that was being delivered vs the proportion that was doing the delivery.  The example I gave above was offering a payload of 10% so for each 1g of cyclodextrin active you added to your formula, 0.1g of it would be ‘active’ and 0.9g would be shell.  That’s OK if the shell is inert and cheap but not so great if the shell is going to change the look or feel of your cosmetic product and/or is very expensive.   There is now encapsulate shell technology available that can delivery in excess of 90% payload such as these colour-containing capsules from Tagra.  This gives formulators added flexibility when developing products, especially in the natural/ organic space where percentage of compliant input is essential for certification (not that this particular example is suitable for organic formulations).   One other development in the encapsulate space is size.  It’s possible to find capsules that are super tiny,  even into the nano-particulate range now. These can make all sorts of products possible as the active may now be technically invisible.  Theoretically one may be able to make a water-clear suspension of retinol or other oil-soluble actives thanks to the magical disappearing properties of nano encapsulation!

A final word.

Putting all of this together we see a technological concept (encapsulation) that has a long history of safe and effective use in the cosmetic field that can both protect our essential oils in the formula (for long-term stability and packaging compatibility) and enhance their (long-term) delivery on (or even through if that’s what you need) the skin.  While this may not be a good fit for all formulations (depending on your formula philosophy, price point or aesthetic),  it seems like a useful thing to know about and experiment with, especially where you are using essential oils AS actives rather than just for their fragrance alone.

What prompted me to look into this again was the launch of a new encapsulated lavender at New Directions Australia.  I have to admit that I’d forgotten how exciting this technology can be! There is some more information about this type of encapsulating material here and on the Tagra website.

Lavender essential oil is Generally Regarded as Safe (GRAS) in terms of its irritation potential. However, that status refers to its un-oxidised or fresh state.  As lavender oil ages the main components, linalool and lineally acetate can oxidise and when they do, they become more irritating to the skin.   Linalool oxidation occurs spontaneously over time when the oil is exposed to air.  There is a link to a paper here in the Contact Dermatitis journal that investigated the increase in allergenic potential between fresh and oxidised linalool.  Here is a link to one paper that looks at the oxidation of linalyl acetate, a process that occurs in the presence of peroxides.  Peroxides can form in a formula as other ingredients break down so it may be that one of your carrier oils starts to go rancid and the free radicals released into the formula because of that kick start the oxidation of linalyl acetate in your lavender.   Robert Tisserand has a good web resource for more information on essential oil stability and it is important to note that there are likely to be subtle differences in how natural lavender oils oxidise vs synthetic fragrances that contain these chemicals but in any case,  Lavender oxidation should be avoided.  I would say that the lengths you go to avoid it and the costs incurred to do so will depend very much on what role the lavender is playing in your finished product (active or just aroma), its dose, the reactivity of the formula as a whole,  who the formula is targeted at (babies and eczema prone individuals should really have all stability precautions taken), leave on or rinse-off and your packaging choice.   The New Directions team put the encapsulated Lavender into a night cocoon sleep mask as the key active so the integrity of the lavender was essential to the finished product efficacy.

Maybe something to put on your ‘to do’ list too whether you are considering it for essential oils or other difficult-to-stabilise actives I’m sure that a solution (or particulate) exists!

Amanda

PS: I am part of the New Directions consulting team and have been for some time but I don’t tend to get involved with the selection of new ingredients or their in-house formulating so what’s new to the showroom is usually quite new for me also 🙂

 

 

2 Comments leave one →
  1. January 25, 2020 3:12 am

    thats so helpful.
    I saved it on my computer to show my husband.
    xoxo
    franziska from powder brows

  2. Earth Digital permalink
    March 28, 2020 6:27 am

    Thank you for you scientific approach – your level of detail and references is very reassuring.

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