Lipids: Oils, esters and silicones

Chemically, oils, esters and silicones are all part of the larger family of ‘lipids’ – emollient substances that are immiscible in water and form a moisture protective barrier on the skin and hair. They may include various plant oils, butters, esters from plant oils and/or mineral oil sources, mineral oils or even silicones. They are added to formulas to help the skin or hair feel softer and conditioned. 

True lipids are hydrophobic – they will not mix with water and need an emulsifier or solubiliser to be incorporated into a cosmetic formula containing water or water-soluble substances. 

And that is where their similarities end, and the differences begin… 

What is the difference?

Plant oils and butters are derived from plant sources, and as such, are considered natural. Plant oils and butters contain a variety of vitamins and fatty acids that can be very nutritive to the skin and hair – so can add to the marketing benefits and performance of a cosmetic formula. However, they can tend to feel a bit heavy and leave a greasy residue if used in significant quantities; this can be balanced with a medium skin feel triglyceride (obtained from a plant oil) or lighter skin feel ester. Interestingly, plant oils and butters are polar lipids – they will not mix readily with non-polar lipids (mineral oils or silicones), and of course will not mix with water, without a suitable lipid stabilising agent.

Esters are created by joining smaller, fractionated parts of different lipids together to create a new material. This is done to create cosmetic ingredients with different sensory and performance attributes. Esters may be made using totally natural oils as the starting source, a combination of natural and synthetic oils, or only synthetic oils. A common example is ethylhexyl palmitate (partially synthetic) or the totally naturally derived coco-caprylate. Esters vary in their polarity – from highly polar materials very compatible with plant oils and butters, to almost non-polar materials, more compatible with mineral oils. You will need to check polarity with your supplier to be sure you are combining compatible materials – or use a suitable lipid stabilising agent.

Silicones are, chemically speaking, based on a siloxane backbone, while mineral oils are hydrocarbon chains. While their starting sources are mined, because of the varying processing steps, they are considered synthetic ingredients. Silicones and mineral oils both come in a variety of molecular weights (based on their chain length and branching) to manipulate their feeling on the skin – but in general, even the heaviest of silicones and mineral oils is still very light. You can even get very low molecular weight materials that are volatile – to evaporate from the skin or the hair – for light application with a weightless finish! Both of these materials are non-polar, and won’t mix readily with plant oils and polar esters with out a suitable lipid stabilising agent. 

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How do you choose which oil, ester or silicone to use?

With so much choice, how do you start to choose which oil, ester or silicone is best to use in your cosmetic formula? 

The first selection criteria is how natural (or not) your formula needs to be. If it needs to be completely natural, then you’ll need to choose a naturally derived ester, plant oil, butter or triglyceride. 

Next, think about what you need the lipid to do in your formula. For example:

plant oils and butters tend to have a heavy emolliency – they can feel greasy and very moisture protective, which is great in moisturisers for dry and mature skin, but not at all suitable in a shampoo for oily hair or a skin cream for a 20-something year old. 

triglycerides and esters tend to have a medium or even light skin feel. These suit younger skin types, as well as Asian skin types. 

silicones and mineral oils tend to have the lightest skin feel of all. These are especially good for younger skins, in foundations, and for those with oilier skin types. 

You can of course mix your choices, just remember to stabilise them effectively if adding water to your cosmetic formula, and be wary of lipid polarity!

So, there you have it, in a nutshell, the differences in the ‘lipid’ family, and how you might pick and choose between the vast array of materials out there. It’s time for you to get creative and explore the world of sensory – and moisture protection – that each class of material provides.