Fats and fatty acids in cosmetics
Fats and oils are an important component of cosmetic products. Whether as the oil phase in an emulsion or as a base in oil products, sticks, or balms – they play a central role.
However, fats are also the starting point for the production of cosmetic raw materials such as emulsifiers, surfactants, consistency agents, and cosmetic lipids.
What is an oil made of?
Oils and fats consist of hydrocarbons – chains of carbon atoms saturated with hydrogen atoms – and are thus organic compounds. Plant or animal fats are chemically triglycerides, but other compounds such as linear esters or saturated hydrocarbons also exist. These compounds are often based on fatty acids or other hydrocarbons. The former are mostly obtained from vegetable oils.
Properties of oils
Depending on the chemical structure or the composition of the fatty acids, the properties of an oil differ:
- Is it liquid or solid?
- Does it spread quickly or slowly?
- Is it oxidation-stable or does it go rancid quickly?
- How well does it absorb into the skin, and what skin feel does it leave behind?
We use these unique features specifically in cosmetic products. This allows us to determine which skin type a product is suitable for, how it feels, and for what purpose it can be used.
For example, a cream for oily skin should contain lighter fats that absorb well and do not leave a greasy shine, whereas the requirements would be quite different for a cream for dry or mature skin. Body products should contain oils that spread well so they are easy to apply, and a hand cream should absorb quickly so you don't have to walk around with greasy hands.
Saturated and unsaturated fatty acids
Most of the oils we use contain fatty acids. These are largely responsible for how an oil behaves. There are saturated and unsaturated fatty acids. In saturated fatty acids, every carbon atom is saturated with hydrogen atoms, which makes the chain straight. Unsaturated fatty acids contain one or more (monounsaturated or polyunsaturated) double bonds. The fatty acid chain can kink at every double bond and is therefore no longer straight. As a result, the molecules of unsaturated fatty acids cannot arrange themselves as well and therefore cannot form solids – they are consequently liquid. In addition, double bonds cause an oil to oxidize more easily.
There are three important rules of thumb:
The longer-chained a fatty acid is, the firmer the oil.
If a fatty acid is unsaturated, the oil is liquid.
The more saturated the fatty acids, the more stable the oil.
For example, butters, such as shea butter, contain a significant proportion of saturated, long-chain fatty acids. These can be imagined like waxes and give a fat firmness and consistency. However, butters also contain unsaturated fatty acids. This mixture creates the typical buttery, spreadable consistency as well as the melting behavior at body temperature.
Coconut oil, on the other hand, contains many short-chain fatty acids and is solid at room temperature, but has a very narrow melting range and easily becomes liquid.
All liquid oils contain a large proportion of monounsaturated or polyunsaturated fatty acids. Therefore, they are considered less stable. One should not heat them to very high temperatures, and they go rancid relatively quickly.
Here is a table of the most important fatty acids:
| Chain | Name | Occurrence examples |
| C8:0 | Caprylic acid | Coconut oil, palm kernel oil |
| C9:0 | Pelargonic acid | Safflower oil |
| C10:0 | Capric acid | Coconut oil, palm kernel oil |
| C12:0 | Lauric acid | Coconut oil, palm kernel oil |
| C14:0 | Myristic acid | Coconut oil, palm kernel oil |
| C16:0 | Palmitic acid | Palm fruit oil, shea butter |
| C18:0 | Stearic acid | Palm fruit oil, shea butter |
| C18:1 | Oleic acid | Olive oil, rapeseed oil, palm fruit oil |
| C18:2 | Linoleic acid | Grape seed oil, safflower oil |
| C22:0 | Behenic acid | Pracaxi oil |
"C" (carbon) indicates how long the carbon chain of the fatty acid is, i.e., how many carbon atoms it contains. The number after the colon indicates the double bonds in the chain – so linoleic acid, for example, is polyunsaturated (specifically diunsaturated).
It is interesting that an even number of carbon atoms predominates in nature. While odd numbers do exist, they are significantly rarer and do not play a major role in cosmetic raw materials.
Hydrogenation (hardening of oils)
Through hydrogenation, unsaturated fatty acids can be converted into saturated ones. This is the case, for example, in margarine production. But it is also interesting for cosmetic products to generate solid fatty acids, which are often used for raw materials such as consistency agents.
Behenic acid, for example, is rather rare and occurs mainly in exotic oils. However, it can be obtained from rapeseed oil, which contains the monounsaturated erucic acid (C22:1). Through hydrogenation (fat hardening), the double bond can be removed, and the saturated behenic acid is obtained. In this way, behenic acid and its derivatives (e.g., behenyl alcohol) can be produced economically in significant quantities.
Palm kernel and coconut oil
What is striking in the table is that some fatty acids, namely those from C8 to C14, are present in palm kernel and coconut oil. Above all, these oils contain lauric acid (C12). Therefore, these oils are also called "lauric oils". There are hardly any other oils in which this fatty acid is contained in a significant amount to make it economically available. However, these fatty acids serve as a basis for the production of surfactants. Therefore, the oil palm is also an indispensable oil source, as it is very high-yielding (six times more than coconut oil!) and other plants could not provide these fatty acids at all.
Here is a list of the fatty acid composition of important fats in %:
| Fatty acid | Palm kernel oil | Coconut oil | Shea butter | Olive oil | |
| C8:0 | Caprylic acid | 3 - 5 | 5 - 9 | - | - |
| C10:0 | Capric acid | 2 - 5 | 6 - 8 | - | - |
| C12:0 | Lauric acid | 45 - 55 | 45 - 52 | - | - |
| C14:0 | Myristic acid | 15 - 20 | 16 - 21 | - | - |
| C16:0 | Palmitic acid | 7 - 10 | 8 - 11 | 2 - 9 | 7 - 11 |
| C18:0 | Stearic acid | 2 - 4 | 2 - 4 | 20 - 50 | 1 - 2 |
| C18:1 | Oleic acid | 10 - 15 | 5 - 8 | 40 - 60 | 55 - 83 |
| C18:2 | Linoleic acid | 1 - 3 | 1 - 2 | 3 - 8 | 3 - 6 |
This table clearly shows how similar palm kernel and coconut oil are, while olive oil and shea butter, in turn, have a completely different composition.
Tropical oils cannot simply be replaced by regional ones!
The short-chain fatty acids caprylic acid (C8) and capric acid (C10) are very popular for the production of cosmetic lipids, as they can be used to create oils that spread very well and have a low viscosity – as is often desired in cosmetic products.
Lauric acid (C12) is usually used for the production of surfactants, as it results in products that clean and foam well.
The solid fatty acids palmitic acid (C16) and stearic acid (C18), in turn, are very popular for processing into consistency agents and emulsifiers, as they bring firmness and stability to a product.
Properties of cosmetic oils
In addition to the fatty acids contained, the properties of an oil depend primarily on its chemical structure:
Triglycerides
Triglycerides consist of three fatty acids linked to glycerin by ester bonds. Vegetable oils and their typical properties are based on the fact that they are triglycerides – they are viscous, slow-spreading, slow-absorbing, and tend to leave a greasy skin feel. If three identical fatty acids are attached to a glycerin molecule, you can recognize this in the INCI by the designation "Tri+fatty acid" (e.g., triolein, tripelargonin, tricaprylin, tristearin, ...)
Examples: all vegetable oils (except jojoba oil), MCT oil (neutral oil), MCT-9, Lipoblend Cushion, Olifeel Pearls
Linear esters
Consist of two fatty components (actually a fatty acid and a fatty alcohol) connected by an ester bond. A natural example of this would be jojoba oil. It is the only vegetable oil that is not a triglyceride. A large proportion of our skin sebum also consists of linear esters. Therefore, jojoba oil is often attributed a certain similarity to skin fats. Very many cosmetic oils (often called ester oils) are also structured in this way. These compounds are significantly lighter and thinner than triglycerides, absorb faster, and spread better. Especially when short-chain fatty acids are used for production.
Examples: Jojoba oil, Coco-Caprylate, Liposens, Hydromollient, SoftEster
Saturated hydrocarbons (alkanes)
Alkanes do not contain any fatty acids at all but are simple hydrocarbon chains – usually saturated. Due to their small molecular size, these oils are very thin and high-spreading. If they are particularly short-chained, they are even volatile, meaning they can evaporate after application to the skin and leave hardly any residue. Alkanes are very typical for mineral oils and waxes, but are also produced from vegetable oils. Long-chain alkanes often occur in natural waxes as well.
Examples: Paraffins (mineral oils), Lipoblend Ultralite, Squalane
Polarity of oils
However, these properties are not the only thing that matters. Depending on the molecular structure or the presence of ester bonds, oils can also be more or less polar – which means more or less water-soluble. Oils are known not to be truly water-soluble, but this shows us how easily they can be emulsified. In addition, oils with similar polarity are easier to mix with each other – oils with different polarity can separate and settle in a mixture.
How polar an oil is must be considered on a case-by-case basis, but alkanes are generally considered to be very non-polar, while linear esters are often highly polar.
Conclusion
It is certainly worth delving into fatty acids and their properties. Often, one can tell from the INCI name how an oil or cosmetic raw material will behave or feel. The study of fatty acids creates a fundamental knowledge base and is a crucial step into the world of cosmetic raw materials and production!
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