In our 'anti-ageing' obsessed world the above terms are impossible to avoid as we all seek active skincare that helps us 'fight off free radicals' etc. But free radicals and oxidation are not just things that speed up the ageing of our skin they also prematurely age our skin care ingredients, well, some more than others and when they do, the chemistry of your whole product changes shortening your products shelf life.
Oxidation reactions in a vegetable oil start when it comes in contact with oxygen from the air and continue until there is no more oxygen left in the product or no more sites in the oil to react with. The speed and impact of these reactions varies depending on your packaging, the oil chemistry and the presence or absence of additional anti-oxidants and as such there is no 'one-size-fits-all' way of solving this problem.
In this article we will look at how the chemical structure of the oil affects its stability.
To illustrate this we will do some simplified oil chemistry. If you are interested in reading more you will find little nuances and additional factors that come into play but in general these rules form the basics of stability.
Vegetable oils are mainly made up of triglycerides which in turn are made up of fatty acids and glycerin. Fatty acids can be organized into three families:
It is common for vegetable oils to contain MANY different fatty acids in their mix and in general the oils containing a high percentage of polyunsaturated fatty acids have the shortest shelf life.
Examples:
Saturated:
Monounsaturated:
Polyunsaturated:
Based on the fatty acid composition of our oils we could assume the following in terms of long-term stability:
Most Stable | MCT Oil (Caprylic/Capric Triglyceride) Coconut oil Olive Oil Palm Oil |
Medium Stability | Almond Oil Cocoa Butter Jojoba Oil Macadamia Nut Oil Shea Nut Butter |
Least Stable | Canola Oil Cottonseed Oil Grape Seed Oil Sesame Seed oil Safflower oil |
If we dig a bit deeper we see that Coconut Oil typically consists of the following fatty acids:
And we see that Grapeseed Oil typically consists of the following:
So, the higher the level of unsaturation, the more unstable the oil becomes.
More and more we are looking for cosmetic ingredients that are good enough to eat and when it comes to edible oils and fats unsaturated oils are much better for our health than the saturated fats typically found in beef tallow, butterfat (goat) or coconut. However, as we have just seen above unsaturated oils are less stable so we have a problem!
There are a few ways to get all of the benefits from the highly active but chemically less-stable vegetable oils while keeping oxidation at bay. Here are our top tips.
Have fun with your oils and remember that even the most oxidatively un-stable of oils still have a shelf-life in excess of one year under most circumstances so with careful handling and good manufacturing processes your blends should be able to go the distance.
Amanda Foxon-Hill
4 July 2012