The term “volatile oil” may sound a little odd, but it is probably the one that best designates a particular type of ingredients in formulation. Why odd? Because the notion of oil is rarely associated with that of volatility. Usually we use the term solvent.
Obviously, oils and fats have been used in cosmetic products since time immemorial. “Cosmeticity”, i.e. the well-known “cosmetic skin feel”, mainly depends on the nature and quantity of fats applied on the skin. Skincare formulation is focused on skin comfort. Makeup products should be long-lasting, and of course, easy to apply. Historically, formulators could play on different factors to adjust these characteristics: the nature and proportion of fats, and the proportion of water in the formula. But it did not leave much freedom. Gradually, another dimension emerged: the “volatility” of oils. It is a rather ambiguous term: “volatile” is often used to describe essential oils, and it has nothing to do with what we are dealing with here. We are talking about a different type of oil. Be it as it may, cosmetics formulation with non-remanent fats emerged: in other words, oils that did not persist on the skin surface started to be used, and we incorrectly called them “volatile” oils. More than oils, we are talking about a different type of fats.
It all started with makeup products, in particular mascaras. Some of the first mascaras were based on a preparation containing Vaseline, like Maybelline’s. This brand’s name is actually derived from the combination of Tom Lyle William’s sister’s name, Mabel, and “Vaseline”. But if these mascaras were easy to apply, they were definitely not long-lasting, because they did not dry: the fatty nature of the film created a deposit on the skin, above and under the eye, which looked quite unsightly. Two long wear solutions were then developed:
- Water-based cake – we are not focusing on this here
- Improved anhydrous formulas
What we are interested in is the second approach. To obtain such formulas, formulators turned to volatile solvents adapted to the waxes used in these preparations in order to create a product which could form a resistant film when drying – similarly to polish. The idea was to use more or less non-polar solvents with a vapor pressure that triggered evaporation at room temperature. One of the first used was turpentine oil, which had properties compatible with key substances: a flash point at 35°C, a boiling point at 160+/-5°C, and a rather high solvency for waxes, in particular beeswax. It was used in preparations sold in tubes with a separate applicator – a brush – before the notion of “automatic” applicator emerged. However, the particular smell of turpentine oil and its safety-related properties – irritability, and in some cases, eye discomfort (stinging) – compelled researchers to quickly find other solutions.
Volatile oils were also used in hair care products, like brillantine. Fatty, vegetable, and mineral oils were often used in styling products called brillantines, or oily creams, like philocomes, a sort of styling ointment which led to products like Pento® or Brylcreem®.
But all these products were greasy and too heavy on the hair. So, gradually, products which were somewhat odd were developed: “petroleum products”. Widely called “lotions based on petroleum ether”, they were meant to reduce the oily effect of the mineral oils used as a base in brillantines. These cleansing or styling hair lotions were based on a hydro-alcoholic mixture to which a small quantity of volatile hydrocarbons similar to kerosene was added.
Other types of ingredients combined with other substances were regularly suggested, like compounds with carbon tetrachloride or carbon disulphide. The cult product in this category was Pétrole Hahn®.
As we have just seen, the first volatile oils contained small fractions of petroleum and represented candidates with interesting properties. Most major “petroleum” suppliers developed solvent mixtures with satisfactory characteristics. These mixtures contained isoparaffins with intermediate molecular weights – C9 to C15 – obtained by cracking petroleum and purified, and their volatility characteristics were those formulators looked for. Their trade names were Solpar®, Isopar®, Shell Sol®, Soltrol® etc., and the first INCI names were also evocative: Spirit of petrolatum distillate, Petrolatum distillate, or Iso-hydrocarbons. These names did not scare anyone at that time!!!
Apart from these particular cases, “volatile oils” were not widely used in skincare and makeup formulas. However, two almost simultaneous events in the 1980s radically changed the situation.
- Brands decided to streamline the use of certain substances and wanted more information about the notion of volatility.
- Volatile silicones emerged.
Volatility: This property is not clearly defined. Volatile substances exhibit a certain vapour pressure related to their flash point. By convention, the value selected by certain developers was a flash point at 100°C. Around these values, the ingredients’ characteristics corresponded quite well to what formulators wanted, although they slightly exceeded the values of turpentine oil, long considered the reference. We are talking about structures with about 12 carbon atoms. These values were also comparable to those of the main volatile silicones, like D4 or D5, which emerged later.
This specification process led to the hydrocarbon mixtures previously used being replaced with much better-defined substances which actually had the same properties: isoparaffins, like isododecane (C12), isohexadecane (C16), isoeicosane (C20), and all their cousins. As volatility declined with an increased MW, formulators mainly used low MWs.
Isododécane ou 2 methyl undecane
The second episode that made things change was the emergence of a new type of volatile oils: volatile silicones. At that time, volatile silicones were new substances – people took interest in them if only because they were new. They completed the arsenal of already trendy silicones and gave formulators the impression that they solved a key issue: skin feel.
The introduction of a new dimension which made the quantity of oil vary over time after being applied radically changed formulation techniques. And that was the role of volatile oils, as could be seen with the emergence, or rather the return of non-transfer makeup products. For a very long time, this property was obtained with soluble colourants. But the problem with this approach was that it lastingly coloured the mucous membrane and prevented the colour from being removed when cleansing. The use of pigments did make it possible to cleanse the skin, but after application, they were mixed on the skin surface with the oily film composed of sebum and the oily phase of preparations. These pigments disappeared due to different factors, like rubbing, wiping, movements, etc. With lipsticks, it was even worse, because the product was partly “eaten”. So, to make them last longer, the idea was to reduce the quantity of remanent fats on the skin surface. But it led to reducing the quantity of fats in formulas, which made application more tricky or incomplete. Volatile oils provided the answer to this contradiction matrix. Before volatile silicones were developed, formulators did have this type of substance at hand, isoparaffin solvents, but they were not or very little used. Plus, their skin tolerance was questioned. So, volatile silicones paved the way for this new type of formulas, both due to their very satisfactory organoleptic properties (smell, taste, and feel), and to their excellent compatibility with the skin. They made application easy and, after they evaporated, the coloured film became concentrated and settled on the skin, which made the products last much longer (time during which makeup remained constant). Given all the applications they made possible, these oils literally invaded the field of formulation on all markets, so much that some formulators incorporated them almost everywhere, sometimes without any reason, and in ridiculously low quantities. Patents multiplied one of the first products of this type. Foundations soon followed, based on the same logic, followed by other products for which the remanent nature of the film was an issue, like sun products, for which the usual sticky effect of fats should be avoided.
However, since nothing is ever over, a few years later, there were debates about the use of volatile silicones. First, the issue of safety by inhalation was raised – and it was never really solved. But the main issue was their classification as VOCs, those air contaminants that accumulate in ecosystems due to their non-degradability. These two reasons made many companies question their use.
That is when formulators rediscovered volatile hydrocarbons as a base to their formulas! That was in the 2000s. Indeed, it was actually possible to replace volatile silicone oils with paraffin derivatives in certain products – with some reservations. Formulas based on isoparaffins flooded on the market! And yet, a new challenge quickly emerged: these hydrocarbons were neither organic nor green!!!!!!
Therefore, in the 2010s, manufacturers, who are always responsive, developed a concept which may sound a little odd: plant-derived alkanes, or bio-alkanes!!! Odd, because nature does not directly make hydrocarbons, let alone volatile hydrocarbons! But the challenge was taken up more or less successfully. Efforts to substitute fish squalane for “plant-derived” squalane helped identify ways to obtain new substances meeting new constraints. If products made of 30 atoms of carbon could be made, it appeared possible to develop products with 15 carbon atoms! In addition, other research resulting from work done on alternative fuels, in particular biofuels, sped things up. The research work done by various players followed different directions as regards processes, but they did have a common point: plant-derived biomass. After much research, several processes emerged. Today, there are different ways to prepare alkanes based on botanical substances.
- Cracking, based on palm oil. This process is derived from the food industry’s techniques. It consists in breaking a complex organic molecule into smaller elements, alkenes, and then hydrogenating them into alkanes.
- Dehydration, based on fatty alcohols: after obtaining a fatty alcohol derived from a plant (for example, coconut oil), the latter is dehydrated to get the corresponding alkane.
- Biofermentation, based on sugars – a sesquiterpene is produced, like farnesol, based on plant biomass (sugar cane, for example), and then it is hydrogenated.
- Metathesis, based on polyols combined with vegetable oils. It is based on vegetable olefins (palm oil) to which a process called metathesis is applied. It was discovered by French scientist Yves Chauvin, who was rewarded with the Nobel Prize in 2005. With a molecular rearrangement, the products obtained are short alkanes, like Tridecane and Pentadecane, which exhibit the expected volatility characteristics.
- Another process results in this type of substances: PICEÒ, for Process Intensified Continuous Etherification. It makes it possible to obtain a substance based on a natural acyclic monoterpenoid, citronellol, which is then derived from the terpenes extracted from the sap of ecoresponsibly cultivated pines to obtain specific polymers. The products obtained are not volatile, but after being mixed with a volatile fraction, the manufacturer manages to produce a substance with volatility characteristics. These products are known as Citropol®. Same idea is developped in EU.
Right now, all these products are alternatives to volatile oils. At least, they are almost always introduced as such. As for volatile silicones, this is only true as regards their volatility. The polarity of substitutes is very different and requires reformulation rather than mere substitution. These substances are more or less volatile, depending on their characteristics, and the study of their behaviour shows they are not all as valuable. Everyone will find something to meet their needs.
Evaporation Curves_BIODEGRADABLE VOLATILE OILS
The main operators are major chemists: Sasol, BASF, Total distributed by Seppic, Amyris by DSM, Clariant, and P2 in the US for citronellol derivatives. And if our French champion BIOSYNTHIS is a bit like an exception in this environment, they do show much creativity with high quality products.
Produceur map: Carte des producteurs de Bio-Alcanes
Another group of substances should be considered in the family of “volatile oils”: perfluorinated compounds, also called fluorocarbons or PFCs, for perfluorocarbons. These particular substances are characterized by different criteria, starting with their insolubility in almost all environments – hydrophilic or lipophilic. This property makes them outstanding lubricants as such or when used to formulate three-phase products. But that is not why they are currently used in cosmetics. They owe their interest to a specific property: their solvency with a few gases, including oxygen, which is why they replaced blood and got called “artificial blood” or “respiratory fluid”. In the cosmetics industry, after a first period in the 1980s, when they were used as emollients, they were revived in the late 2010s in particular formulas: post-foaming products. They actually enhance formulas’ bulking when using the product due to specific varieties of perfluorinated compounds with quite high a vapour pressure. For example, the product range called FiflowÒ was based on perfluorohexane. According to the manufacturer, it had an anti-ageing positioning, since this substance could provide the skin with oxygen. This approach was little documented in terms of outcome, so these ingredients were not promoted for their solvency or volatility properties. Lastly, these substances are subject to different regulatory provisions. PFCs are one of the six main greenhouse gases on the Kyoto Protocol list, and they are also mentioned in Directive 2003/87/EC. All the users have to be aware.
This concept of volatile oils therefore corresponds in cosmetics to a specific use. The easiest would be to use simple products like volatile alkanes. But why make it simple when you can make it complicated. Other substances have been “invented”. One cannot but question the nature of these products. Introduced as plant-derived alternatives to synthetic products and called “bioalkanes”, they are almost all strongly dependent on processes derived from the most academic chemical industry. We are far from the notion of natural products, let alone organic products: whatever the classifications and different recognition levels of standards which are all equally questionable, everyone should question their nature. Obviously, there are a lot of inconsistencies between the processes used to obtain these ingredients and the way they are introduced.
However, they are functional and their safety of use is very satisfactory. So, let’s not be more Catholic than the Pope!!!!!!
What should we think about all this? It is both good and bad.
- Bad, because ingredients are introduced in a way that does not reflect what they truly are. If their origin is natural, even biotechnological, chemistry does play a major role in the processes used. At the end of the day, they are much modified and have nothing to do with the initial ingredients.
- Good, because this story highlights the incredible creativity of chemists and chemistry’s resources to make ingredients that meet ever-changing expectations due to the evolution of genres and concepts.
Ultimately, if we stopped opposing nature and chemistry, we would be better armed to take up tomorrow’s countless, sometimes contradictory challenges.
I want to thank all contributors to this post, in particular cosmetician Biosynthis, a pure player in this often too synthetic, “great chemistry”-oriented world.
Thanks for reading this post.
Jean Claude LE JOLIFF
Learn more: Biblio et Webographie Huiles volatiles
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