[Back to the previous article: Physical properties and impact on the final product]
In this final article about emollients, we will talk about how to design the fat side of our products.
- How much fat should we add to the formula?
- How do we combine emollients in the formula?
- Final table with emollient characteristics
So we have seen that emollients can have different physical and chemical properties and influence on the final cosmetic product. How do we decide the combination of emollients in the oil phase of our creams, then?
I think we can say we have to make two basic decisions when designing our oil phase with emollients: (1) How much fat do we want to use (the overall percentage of emollients in the cream), and (2) How do we distribute different emollients in the formula.
How much fat should we add to the formula?
The intuitive answer to this question is: less fat for oily skin, more fat for dry skin, and overall less fat for face creams, more fat for body creams.
But how much exactly? I checked on handbooks, patents, and scientific papers, and I didn’t find a clear answer. Then I went to less-rigorously scientific sources, that is, blogs about formulation and DIY cosmetics, and the information I found was scattered and different from blog to blog and, in particular, from country to country.
I found out that Germans are the ones who like to have the highest fat percentage in their creams. I’ve seen body creams with up to 35% fats and face creams with up to 20% (11). The English website Making Skincare suggests 3-8% fats in face creams for oily-normal skin, up to 12% for body creams and face creams for dry skin, and up to 20% for body butters and creams for very dry skin (12).
I was not very satisified with these scattered percentages, so I looked for some formulas and made an average of all the data I could find. I took recipes from the German websites Olio Natura (and Heike Käser’s related book) (11, 13), Meine Kosmetik (14), and Spinnrad (15), from the Canadian blog Humblebee & Me (16), the New Zealand Naked Chemist (17), and from the American Point of Interest (18), in addition to Making Skincare (12).
My conclusion is that the overall range of fats in lotions and creams goes from 3% to 35%. For face creams, the typical range is from 3% to 17-20%, whereas for body creams it goes from 12% to 35%. Hand creams are somewhere in the middle, ranging from 5% to 20%.
For “fats” here I mean the whole stuff: vegetable oils. vegetable butters, squalane, and tocopherol. I didn’t count waxes and consistency factors in this average, although these ingredients have emollient capability as well.
How do we combine emollients in the formula?
As discussed above, emollients are characterised by a certain viscosity and consequent spreadability and skin feel. Some are slowly spreadable with greasy/heavy skin feel, others are fast spreading, fast absorbing and with light skin feel.
This doesn’t mean that for a light lotion we should only use “light” emollients, because the resulting product will be too thin and unstable. It is necessary to have some body also in light creams.
So the best thing to do is distributing the emollients, such that there is a “representative” of each group.
This is quite obvious if you understood something about rheology (yes, I’m obsessed with this rheology thing), yet I haven’t found precise “rules” on how to build an emollient mixture. Probably because there is none and there are several approaches and theories about it.
The cascading theory
In Italy, people often speak of the emollient cascading as if it were a rigid and absolute rule. I’ve seen people being mortified online because their recipe didn’t follow some rigid percentage rules (which I ignore, I have to say) and this automatically made their formula “nonsense”.
I searched the internet for a scientific guide about this “rule”, but I found out that the emollient cascading is one of the many theories that were proposed as an approach to emollient formulation. The only references with plots and data that I could find are (19) and (20), but it’s not like they give real guidelines concerning percentages. They just state what would be self explanatory, if one understood the rheology of fluids.
I think that the best way is to test some combinations of emollients and give “priority” to lighter or medium-high viscosity emollients according to the need of the cream.
- Solids: in this regard, we have to consider the presence of solid butters (cocoa and shea butter in the table below, but there are others – kokum, mango, murumuru…) and of solid esters, waxes and fatty alcohols (cetyl palmitate, cetyl alcohol, cetostearyl alcohol, beeswax…). As already discussed, the presence of solids make the cream thicker, firmer and improves stability. Concerning the skin feel, they can differ:
- Some butters (like shea butter) spread slowly but not incredibly slowly. Shea butter is rather soft and perceived as very emollient and “nourishing” on the skin.
- Other butters, like cocoa butter, are harder and very slow spreading.
- Waxes are slow spreading and relatively dry. Be careful when you use them and don’t add them in too high amounts.
- The effect of solid esters can vary according of the ester itself. For example, cetyl palmitate is waxy and not greasy, rather dry. It adds body to the cream but doesn’t add greasy feeling. The same is true for cetyl ricinoleate.
- Fatty alcohols like cetyl alcohol are very similar to cetyl palmitate. They give more body to the cream but they are not greasy.
- Heavy emollients are high viscosity fluids. They make the cream heavier, improve stability, decrease spreadability. Good for thick/heavy creams, but a little percentage is useful also in light creams. Even in thick/heavy creams they are however not the main emollient (they would make the cream too tough to rub in).
- Medium emollients are… in the middle. They spread well, they are in the middle between heavy and light. In most cases they are the ones present in highest percentage.
- Light emollients are low viscosity fluids. They spread fast and leave very thin or no residue on the skin. Thus, they are perceived as “fast absorbing”. Their percentage depends on how you want the cream to be (lighter or heavier), but as always, a little amount should be there also in heavy creams.
For other tips about the adjustments you could make to your formulas, you can also visit the Making Cosmetics website at Reff. 21 and 22.
I mentioned many times that, at least in Italy, there is the wrong habit to make this kind of distinction based on the density of emollients. This leads to some misleading information that I read around in the Internet, like:
- Caprylic-capric triglycerides: based on density they are thought to be medium- if not heavy- emollients. Actually they have low viscosity so they are rather medium-light.
- Linseed oil: based on density it is often placed alongside castor oil in the heavy oils. Guys, have you ever touched linseed oil and compared it to castor oil? Come on! The viscosity is definitely lower than that of castor oil or tocopherol, it is NOT a heavy oil!
So in the end, one possible approach to distribute emollients could be this:
1- Establish the overall amount of fats: solids (butters) and liquids (vegetable oils, tocopherol, squalane, etc.)
2- Establish the amount of solids. For this, you should take into account if consistency factors (waxes, cetyl alcohol, cetyl palmitate) are present in the formula. Typically, the solid butter amount in creams range is 0-10%.
3- Establish the liquid emollient distribution. For example, you can start by dividing the three “categories” (high-medium-low) into equal parts and then balancing them according to the effects you want to get. In most cases, the class of oils that will be present in highest percentage will be the medium one and the class present in lowest amount will be the high viscosity one. The low viscosity emollient class is the one you can balance against the medium viscosity one to achieve a certain effect.
But ok, don’t become paranoid about this thing: it’s just a possible approach. You will learn much more if you just try different combinations, keeping in mind the viscosity part and the solid percentage, and touch with hands what a certain combination feels and looks like. It’s really difficult to predict and understand the skin feel of a mixture just by reading the composition on paper, it’s much better if you directly test it.
Don’t feel bad if people on the internet tell you that your “cascade” doesn’t make sense. They probably think that linseed oil is as heavy as castor oil.
Moreover, there are also other approaches. For example, Germans like to talk about Basisöle (basic oils, that are not thermosensitive) and Wirkstofföle (functional oils, with specific and important properties for the skin, typically thermosensitive). They all count in the overall fat phase percentage, and typically there is at least one Wirkstofföl in every formula.
As an example, the well-known German website Olionatura (at least, well-known in Germany) divides vegetable fats in these two groups and then in subgroups mainly depending on their stability to oxidation – that is, on their fatty acid composition (prevalence of saturated, monounsaturated or polyunsaturated acids) (11, 23).
This means that we have a group of Basisöle that is stable to oxidation (like Jojoba oil, caprylic-capric triglycerides, squalane, broccoli seed oil – the Germans love it, it’s in EVERY hair product), a large group that is a bit less stable but still OK because of the prevalence of oleic acid instead of linoleic/linolenic (olive oil, almond oil, Argan oil, rice bran oil), and a group that is less oxidation stable because of the high level of unsaturation (sunflower seed oil, safflower seed oil, grape seed oil, wheat germ oil, and the king of unstable oils, linseed oil). Then we have the solid groups, that are divided into long-chain ones (shea, mango, cocoa butter) with slow spreadability, and the short-chain ones (like coconut oil) with higher spreadability; both groups are oxidation stable.
Finally, we have the Wirkstofföle, the ones that have very cool properties for the skin but are typically not only oxidation prone but also temperature-sensitive. Here we can find hemp seed oil and rosehip oil, for example.
In a formulation, they typically pick up one representative for each of these groups, with the Basisöle of the “stable” and “bit less stable” groups being used in larger amount in the formula, followed by solids, then unstable Basisöle and finally Wirkstofföle.
I believe this is an interesting classification, although it takes only marginally into account the spreadability and sensory properties of the mixture.
As always, the best way is in the middle: a curious and experimental formulator would take both approaches (the cascading and the composition-based one) and try to make the best out of them.
Final table with emollient characteristics
Here is what you came for: a table with physical characteristics of some emollients. References for each oil are listed below (24-39). If the source is not specified, it is the Wikipedia page (English version) relative to the specific substance.
I could not find reliable data for all the emollients in the list. If I will find them, I will update the table. Or if you find them, feel free to share the source with me. Keep in mind that it is not easy to find reliable scientific work about vegetable oils and organic cosmetics in general.
You see, scientific papers are generally published by academic researchers (the ones who work in universities). Most of the cosmetic research is however made by companies, therefore it is more common to find patent applications than peer-reviewed scientific work. The few people who do research about cosmetic science don’t make it to high impact factor journals because cosmetics is not a very trendy topic. And being trendy is everything in academic research, trust me.
Ok, that’s all for now!
As you can see, this was the result of a huge work and I have put a lot of time and effort in finding reliable references for everything I have written. If you found mistakes or wrong data, please let me know!
If you found this articles useful, feel free to tell your friends about it! But please, PLEASE, don’t copy and paste my content without crediting me as author and linking to my blog. I believe in free sharing of scientific knowledge, but please show some respect for this work, that I have made for YOU and for FREE!