by Amanda Foxon-Hill
It was during a conversation a week ago that I became aware of a potential…. let’s say ‘situation’ can occur with Oleic Acid. Oleic acid is commonly found in vegetable oils and is a major component in each of the following oils where it may account for up to 80% of the fatty acids present:
The situation is that Oleic Acid is a known penetration enhancer and as such has been widely studies by the Pharmaceutical industry as a potential vehicle for delivering actives through the skin. This research showed that Oleic acid works in two key ways, firstly by helping to solubilise the active – a better solubilised active will penetrate better and secondly by damaging the skin barrier – a weak skin barrier is easier to penetrate so watch out eczema prone-folk! The second mode of action rang alarm bells with me and many others in the cosmetics industry as damaging the skin barrier is NOT something we want to achieve and while Oleic Acid has been classified as irritant rather than down right mutant it is still worth keeping an eye on.
So, does that mean that the oils listed above that are high in Oleic Acid are damaging to the skin?
Well. I initially thought so but then I stopped and though on……
When we say ‘oleic acid’ are we talking about the same beast?
A little bit of digging and a dash of experience shows me that the Oleic Acid ‘fatty acid’ in a fat is part of a triglyceride. This means that the oleic acid is attached at one end to a molecule of glycerine – a glycerine molecule that also has two other fatty acids in its grip.
A Triglyceride looks like this:
The process of breaking triglycerides up is called Hydrolysis (hydro= water, lysis = splitting or something Latin) (found on this website)
- I know that Oleic Acid is a penetration enhancer because I have seen plenty of evidence of that and it has a long history of use in the pharmaceutical arena.
- I know that Oleic acid is present in some vegetable oils BUT not usually as the free acid, as part of a triglyceride.
- I know that triglycerides can be broken down relatively easily.
My questions then became:
- Does Oleic Acid in a triglyceride have the same skin penetration properties as FREE oleic acid?
- Does Oleic Acid in a triglyceride have the same irritation potential as FREE oleic acid?
- How much FREE oleic acid is usually floating around in a vegetable oil?
- Does the amount of FREE oleic acid in a vegetable oil change over time in any way?
The flighty part of my thinking process decided that rather than go through my own questions in order I should just check out point three first. After all this might be something that oil manufacturers measure and it makes sense to start off by comparing apples with apples (and here the apple is FREE OLEIC ACID).
It didn’t take long to find out that Virgin Olive Oil has a provision for free Oleic Acid – it has to be kept to below 0.8% (at least here in Australia it does) of the oil to pass. Standard Olive Oil can have up to 2% Oleic Acid before it is failed. This was both interesting and encouraging as such a small level probably means that I don’t have to worry too much about Olive Oil damaging my skin barrier……
Apparently too much free Oleic Acid can alter the taste of the oil. It’s presence is also a sign of poor fruit handling or frost damage which is also interesting.
I found a level of 0.05% Free Oleic Acid in a specification for Sunflower Seed Oil (high Oleic Acid grade) and values ranging from 0.5-3.7% in Canola oil depending on how it had been processed and its age.
From doing this I confirmed my suspicions that Oleic Acid content does rise over time – it is part of the ‘going rancid’ process, that it can vary depending on how the oil is distilled and that it changes from season to season. Free Oleic Acid can be formed in any oil that has an oleic acid based triglyceride and its presence can be hastened by the usual suspects – heat, UV light, oxygen, water but also before that from a poorly managed crop or distillation process.
So that’s questions 3 and 4 answered but what about 1 and 2?
To answer the question (in my head) about skin penetration potential of the Free Fatty Acid vs the Triglyceride I have to think both about the Free oleic acid chemistry and about the barrier damaging potential. I feel that we can get the barrier damaging potential out-of-the-way quickly – a vegetable oil is complex and oily and as such is quite likely to sit on the top of the skin and hydrate it by preventing moisture loss. This SHOULD help to maintain barrier function. In addition most vegetable oils contain skin-friendly antioxidants, soothing agents and Omega fats which also aid in building a better barrier. So, I would not expect the oleic acid rich oil to be as damaging as the free oleic acid….
Oleic Acid stick model from Wikipedia
When I see this I start to see why the triglyceride Oleic Acid is most likely no problem at all in terms of skin irritation. The functional group of this chemical is the O and the H. This is the acid part. The double bond on the kink in the middle is also important but less so than the head. In a triglyceride this functional head group is clinging on to glycerine so unless it drops that the fat is going to be nothing more than fatty and can’t really disrupt any barrier.
But would it still encourage skin penetration?
This is where it gets a little more difficult and where I have to stop for today. While I have managed to get a bit more insight into some of my questions this one now has me perplexed. I have read much about the skin penetration improvements seen with things like vegetable and animal oils vs mineral oils but have never managed to work out the what’s and why’s exactly. After all skin penetration can be enhanced in many ways (we have looked at two of them today).
So I think that the best thing to do is to come back to this later once I have had time to do a bit more reading.
But in the meantime it looks like we can use high Oleic vegetable oils with confidence just as long as the FREE oleic acid content is relatively low – we should be able to find that information our from our oil suppliers and can help things along by storing our oils correctly and using whilst fresh!
I love science, don’t you?