Sophie Cambos, Florence Clémeceau, Emmanuelle Mérat, Alicia Roso, Juanshu Shen
2014, 28th IFSCC congress
Oils or emollients are some of the first components in skin care formulations, especially in emulsions. There are often use at high percentages and listed just after water which is generally the first component. Many studies have been done to characterize and understand the properties of emollients1 and it is well known that the oily phase plays an essential role in the perceived moisturized sensation on skin. Emollients can indeed act as occlusive agents (preventing of Trans-Epidermal Water Loss2) as well as influencing the perceived comfort sensation by maintaining a soft and smooth skin feel3. However, depending on their origin and structure, oils can be more or less biodegradable. Some of them are classified as persistent and can accumulate in the environment. More over, the refining process in oil production can also generate significant waste. For a more sustainable approach, that preserves resource availability, and from an economic perspective, there is a need to reduce the amount of oils or emollients in cosmetics while giving the same perception of emollience. The purpose of this study is to investigate the influence of the emulsion type and the emulsifying system on the perceived emollience, while keeping similar ingredient composition (emollient, thickeners and additives). The final idea is to select, from the comparison at different oil levels, the emulsion type that provides the same perceived emollience with a significant decrease in oil concentration. The emulsion’s manufacturing process impact on the energy consumption will be also considered.
Materials and Methods
- Raw materials and formulas In order to study the perceived emollience, several simple emulsions chassis are considered: oil in water, water in oil, High Internal Phase Gel-in-oil4,5, comparing glycosidic emulsifiers and traditional benchmarks. To allow tentative connections with the formulation type as well as with the emulsifier nature, the emulsions are realized in closest composition: same emulsifier concentration, same oily phase (with various concentrations), same thickener and additives. The manufacturing procedures are optimized for each emulsion chassis to reduce the energy consumption while keeping a good stability over time (favoring a cold process and the lowest mixing energy). The stability at one month of storage at room temperature and 45°C is considered as a minimum requirement.
- Emollience evaluation *The perceived emollience and aesthetics of the optimized emulsions are assessed with a sensory analysis method by 10 experts. *The occlusive character of each emulsion is evaluated in vitro, according to Handjani-Villa6 test, in which a gelatin layer models the stratum corneum. The water loss is measured from the gelatin cells submitted to a relative humidity gradient, before and after application of 20mg of cosmetic formula to its surface (± 0.5mg corresponding to 2.8mg/cm2).
Summary of the results
The training on emollience evaluation was easy for all the panelists, leading to a reliable validation step. The final sensory evaluation demonstrates the same perceived emollience between the high internal phase gel-in-oil (Geltrap proprietary concept) containing 10% of oil and the O/W emulsions containing 20% of oil (same nature). More over, surprisingly, in the same conditions, the high internal phase gel-in oil formula provides similar emollience than the classical W/O emulsion containing double the quantity of oil (20%). However, thanks to its high quantity of water and to its strong shear thinning profile, the gel-inoil formula gives a first fresh sensation with a light skinfeel, different from the classical W/O emulsion.
Despite the common emollient fatty phase, the occlusive character is obviously influenced by the emulsion type. When comparing the formulas containing with the same xyloside emulsifier at 10% of oil obtained by different manufacturing procedures, the high internal phase gel-in-oil (Geltrap proprietary concept) provides significantly higher occlusivity than the cream gel. More over, the occlusive character obtained with the gel-in-oil at 10% is equivalent to the one provided by the classical W/O emulsion containing double the quantity of oil (20%); This result is consistent with the previous sensory evaluation. As far as the manufacturing process of the emulsion is concern, the cream gel and the gel-in-oil concept are the easiest to create, at room temperature and with a low mixing energy contrary to the common W/O emulsion.
The aesthetics, as well as the emollience perception are obviously influenced by the formulation concept, even for formulas with similar compositions. Irrespective of the emulsion type, water in oil or oil in water, the glycosidic emulsifiers shared a common soft afterfeel compared to the benchmark. Among the tested formulas, the High Internal Phase Gel-in-Oil concept is the only formula that can be manufactured both with a cold procedure and a reduced mixing energy. More over, without compromising aesthetics, the gel-in-oil formula provides similar emollience with only half the fatty phase in comparison with the other emulsions. This study opens perspective to save resource availability and improved emulsion sustainability that will need to be completed through biodegradability measurements.
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5- J. Guilbot J. and al.. Oil in water emulsion having improved sensory properties, Seppic, WO 11015759, 2011.
6- Handjani-Villa R.M., Rondot B., Lachampt F. Measurement of the moisturizing effect. Cosmetic and Toiletries, 1976, 91, 11, pp25-30.
Seppic, 22 Terrasse Bellini – Paris La Défense, 92800 Puteaux, France