The hydrolipidic film covers the surface of the skin and actively contributes to the skin surface smoothness and the skin barrier function. We have developed a biomimetic ingredient of the hydrolipidic film as per its fatty acid profile.
Ethylhexyl olivate (INCI nomenclature) brings clinical benefits for numerous parameters and rheology advantages to the formulation. One single application of a formulation containing 3% ethylhexyl olivate was shown to significantly increase skin hydration (+12.2%, p<0.05), barrier function (+16.7%, p<0.05), visco-elastic properties (+6.7%, p<0.05) and skin surface profilometry (+11.2%, p<0.05) for up to eight hours. In another experiment, ethylhexyl olivate was compared to 10 different oil/emollients and ranked third for the viscosity enhancement and second for spreadability index on skin. Thanks to its molecular composition, ethylhexyl olivate creates a subtle veil naturally integrating itself within the hydrolipidic film and significantly improving skin sensorial properties. Ethylhexyl olivate stands as a key tool for formulation chemists while positively acting on skin physiological features as well as on sensorial properties. As an extension of the ethylhexyl olivate ingredienty line, we have added the ingredient, dodecyl olivate. The physical particularity of this ingredient is a longer carbon chain compared to ethylhexyl olivate with a slightly higher degree of saturation. Such physical characteristics endow dodecyl olivate with a melting point in the range of 25°C-30°C that is in the vicinity of the skin surface temperature. In addition to obvious superior sensorial properties, dodecyl olivate brings clinical benefits for the skin barrier function (+17.8%; p<0.05) and skin visco-elastic attributes (+7.1%; p<0.05).
The skin is externally located and thus serves as a sheath separating internal organs from a direct contact with the environment. The main roles of the skin are: protection from UV radiation (melanogenesis), immune defence and a barrier function preventing the penetration of foreign particles. Perhaps of greater importance, skin – especially the stratum corneum layer – is dynamically involved in the management of internal water levels.1 The first skin layer facing the external environment is the stratum corneum; the outermost layer of the epidermis. This histological section is predominantly represented by keratinocytes. The epidermis is constantly renewed through an upward flow of keratinocytes originating from epidermal basal layers up to the stratum corneum. The stratum corneum accounts for most of the permeability barrier that is mainly provided by the organised embedding of keratinocytes into a lipid-rich extracellular matrix. Chemical analyses have shown that the intercellular lipids of the stratum corneum are mainly composed of ceramides, cholesterol, cholesterol esters and fatty acids themselves synthesised by the keratinocytes. In addition to the intercellular lipid lamellae, other classes of lipids originating from the skin surface also play important roles in the stratum corneum. The thin sheet formed by those lipids is called the hydrolipidic film and contains fatty acids.2 Activation of the PPARs has been shown to be involved in keratinocyte differentiation10 and accelerated barrier function recovery following acute barrier abrogation.11,12 While secreted at the outer surface of the epidermis, hydrolipidic film lipids may also be importantly involved in the maintenance of the integrity of the lipid configuration of much deeper layers of the stratum corneum. Numerous studies have demonstrated that, depending upon the category of lipids, a gradient of skin surface lipids is detected across the stratum corneum.3-8 It is also proposed that lipids from the hydrolipidc film penetrate within the stratum corneum intermixing with the lipid matrix (cholesterol, ceramides and fatty acids) into which keratinocytes are embedded. This would improve the skin barrier integrity supporting better skin texture and enhanced skin hydration and visco-elastic properties. The aim of the present study was to investigate the dermatological compatibility and clinical efficacy of a technology based on a skin-like, naturally-occurring, fatty acid composition. The ingredient used in this study, ethylhexyl olivate, is a complex combination of fatty acids, chemically similar – biomimetic – to the hydrolipidic film. This ingredient was shown to bring benefits for the skin barrier function. In turn, the pro-barrier action of ethylhexyl olivate demonstrated positive effects for skin hydration, skin elasticity and skin surface topography. Clinical results obtained with dodecyl olivate will also be discussed.
Materials and methods
The effect of ethylhexyl olivate on formulation viscosity was tested in the following mixture: 7.5% ethylhexyl olivate or other oils/emollients to be tested; 5% cetearyl olivate (and) sorbitan olivate (emulsifier); 2% glycerin; 0.3% xanthan gum; preservatives and water up to 100%. Formulation viscosity was measured with a Brookfield rotational Viscometer using appropriate spindles at 20 rpm for 1 minute. The quantification of the effect of ethyhexyl olivate and dodecyl olivate on skin moisture was achieved using the Corneometer CM 825, Courage+Khazaka GmbH. This measurement is based on the different dielectric constant of water (81) and other substances (mostly<7). The measuring capacitor shows changes of capacitance according to the moisture content. During the measurement an electric scatter field penetrates the very first layer of the skin and determines the dielectricity. Trans-epidermal water loss (TEWL) was assessed using the Tewameter 300, Courage+Khazaka GmbH. The measurement of the water evaporation through the epidermis is based on the diffusion principle in an open chamber. The water density gradient is measured indirectly by the two pairs of sensors (temperature and relative humidity) inside the hollow cylinder and is analysed by a microprocessor. Skin elasticity was measured using the Cutometer MPA580 (Courage+Khazaka GmbH). The measuring principle is based on a suction method. Negative pressure is created in the device and the skin is drawn into the aperture of the probe. Inside the probe, the skin penetration depth is determined by a non-contact optical measuring system. The light intensity varies due to the penetration depth of the skin into the probe. The resistance of the skin to be sucked up by the negative pressure (firmness) and its ability to return into its original position (elasticity) are displayed as curves at the end of each measurement. From these curves the general visco-elastic properties of the skin can be calculated. The Visioscan VC98 (Courage+ Khazaka GmbH) consists of a highresolution UV-A light video camera. The camera is connected to a computer and allows for the digitisation of the skin surface topography.9
Results
Olive oil exhibits a fatty acid composition physiologically close to what is found in the hydrolipidic film covering the surface of the skin. We have developed a method by which olive oil can be utilised as a starting material to produce cosmetic ingredients. This is achieved while maintaining the molecular integrity of the oil. The peculiarity of those ingredients is that they are composed of a combination of fatty acids that chemically – and physiologically – mimics what is found at the surface of the skin (Table 1). Oil extracted from the olive fruit under specific conditions is the only one providing such a “skin-like” fatty acid composition. As mentioned previously, skin surface lipids have this ability to penetrate the inner layers of the stratum corneum, integrate into the intercellular lipid lamellar matrix and become part of the barrier layer. By using a fatty acid composition that mimics that of the hydrolipidic film, it thus becomes possible to take advantage of its natural “entry pass” to access inner layers of the stratum corneum. Therefore, in using olive oil as a starting material, we succeeded to derive cosmetic ingredients, such as ethylhexyl olivate, endowed with a physiological action through natural affinity with the lipid matrix of the upper layers of the epidermis. A skin diagram showing the presence of the hydrolipidic film at the surface of the stratum corneum and its diffusion into the lipid interstices embedding the keratinocytes is shown in Figure 1. We first looked at the effect of ethylhexyl olivate when added in a formulation. Ethylhexyl olivate was compared to 10 different oils/emollients and ranked third for the viscosity enhancement and second for spreadability on skin (Fig. 2). The oils/emollients tested are shown on the left side of the graph. Skin spreadability was assessed by two independent experts in a blind fashion. Spreadability scores (ranging from 1 to 11) are shown on the right hand side of the bars. Ethylhexyl olivate is appropriate to create a high level of viscosity while maintaining a superior spreadability index on the skin. Indeed, ethylhexyl olivate provided a viscosity level similar to what can be obtained using squalene or squalane. However, a drawback of those two ingredients was the poor spreadability score. Ethylhexyl olivate obtained the second best spreadability score next to cyclomethicone. Ethylhexyl olivate was then tested for its ability to enhance skin hydration. Formulations containing 5% ethylhexyl olivate or the same concentration of an olive oil-derived unsaponifiable fraction enriched in squalene were applied topically on the forearm of 10 volunteers. A squalene fraction was chosen as a comparator as it is also an important natural lipidic component of the hydrolipidic film (Table 1). Skin hydration was measured at baseline prior to formulation application and at times 30 minutes and 120 minutes postapplication. The application of formulations containing either ethylhexyl olivate or squalene improved skin hydration to the same level when the corneometry measurement was performed 30 minutes upon formulation applications (Fig. 3, p<0.001 vs. untreated skin site). However, only the formulation containing ethylhexyl olivate succeeded in sustaining the hydrating effect for up to two hours post-application. At that time, squalene had lost more than 50% of its efficacy. In fact, the hydrating action of ethylhexyl olivate and that of squalene were significantly different (p<0.005) at time point two hours post-application. This could be explained by a broader coverage of the hydrolipidic film – and enhanced barrier function – in the presence of ethylhexyl olivate. The long-term efficacy of ethylhexyl olivate was verified for hydration, elasticity, barrier function/transepidermal water loss (TEWL), and surface smoothness on 20 volunteers. In this trial, one single application of a formulation containing 3% ethylhexyl olivate was performed at time 0 (baseline) and all parameters were measured 1 hour and 8 hour post application. Results have shown that one single application of a formulation containing 3% ethylhexyl olivate significantly increased hydration (Fig. 4, p<0.001 vs. control), elasticity (Fig. 5, p<0.001 vs. control), reduced TEWL (Fig. 6, p<0.05 vs. control) and improved skin surface smoothness (Fig. 7b, p<0.05 vs. control). A digitised micrograph of the skin surface texture at all experimental time points (baseline, 1 hour and 8 hour post-application) is shown in Figure 7a. A clear reduction in skin dryness and flakiness was observed upon application of the formulation containing ethylhexyl olivate. This observation is in agreement with the skin surface topography quantification shown in Figure 7b. For all parameters tested, there was no significant difference (p>0.05) between the effect of the formulation containing ethylhexyl olivate at time 1 hour and 8 hour. Those results demonstrated that the efficacy of ethylhexyl olivate can be maintained up to 8 hours after one single application. Dodecyl olivate is another ingredient derived from the olive chemistry and has been engineered to reach a melting point in the range of 25°C-30°C that is similar to what has been reported for the skin surface temperature.13 This physical property of dodecyl olivate positions it as a highly compatible fatty acid composition for skin and hair applications. In addition to possess superior sensorial attributes, dodecyl olivate was awarded the ECOCERT status. Clinically, dodecyl olivate was shown to improve the skin barrier function by significantly reducing the transepidermal water loss when measured 8 hours after one single application (Fig. 8, p<0.001 vs. control). The potential gain in hydration led by an improved barrier function translated in a significant increase in the visco-elastic properties of the skin (Fig.9, p<0.005 vs. control). In a self-assessment trial, 95% and 90% of subjects gave high scores for skin spreadability and the absence of stickiness, respectively, upon the application of a formulation containing 3% of dodecyl olivate.
Conclusions
Ethylhexyl olivate is a biomimetic of the hydrolipidic film covering the surface of the epidermis and capable of intermingling with the lipids of the stratum corneum barrier. This unique property of ethylhexyl olivate allows for various benefits such as formulation textures, sensorial advantages as well as clinical efficacy. Indeed, ethylhexyl olivate is capable of building a high viscosity level in formulation while preserving an excellent spreadability index. Furthermore, the action of ethylhexyl olivate is sustained in time. One single application of ethylhexyl olivate maintained significantly higher levels of skin hydration, skin elasticity, skin barrier function and skin surface smoothness for up to 8 hours post-application. Those results position ethylhexyl olivate as an ingredient for “all-day moisturising” concepts. Thanks to its molecular composition, ethylhexyl olivate creates a subtle veil naturally integrating itself within the hydrolipidic film and significantly improving skin sensorial properties. Ethylhexyl olivate stands as a key tool for formulation chemists while positively acting on skin physiological features as well as on sensorial properties. The new member, dodecyl olivate, produced significant clinical benefits for skin barrier function as well as for skin visco-elastic properties. Its skin-like melting point becomes interesting especially in terms of skin sensorial properties and skin spreadability. Dodecyl olivate shares the same 8 hour-sustained effect as observed in the case of ethylhexyl olivate for the parameters of skin barrier and skin elasticity. Its ECOCERT status widens its use in all natural and green formulations. Ethylhexyl olivate and dodecyl olivates both stand as a key tools for formulation chemists while positively acting on the skin’s physiological features as well as on sensorial properties.
References
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