330 JOURNAL OF COSMETIC SCIENCE TI-m CONTRIBUTION OF EMOLLIENTS AND EMUSIF1ERS TO SKIN EFFICACY Johann W. Wiechers, Ph.D. Uniqema, PO Box 2, 2800 AA Gouda, The Netherlands Cosmetic skin care formulations without emollients or emulsifiers are hardly conceivable. Emollients have been used for centuries to impart a specific skin feel as well as for their secondary skin efficacy benefits such as skin moisturization and elasticity. Whereas the first reason fbr using emoIlients remains unchanged, the second reason is gaining importance with the current strive towards ever more efficacious cosmetic products. For this reason, we measured many personal care ingredients for their performance towards three skin effects: moisturization, elasticity and substantivity. Non-formulated emollient was applied to the skin and left for a time up till 6 hours after which the product was removed (moisturization and elasticity) and the effect measured by non-invasive skin bioengineering techniques. This revealed that these emollients had a wide range of efficacy towards these activities. Their performance was expressed relative to untreated skin (0%) and a benchmark product-treated skin (100%). Using artificial cut-off values at 30 and 70%, this relative performance testing allowed the identification of low (30%), medium (30-70%) and high performing (70%) ingredients (see Figure 1). When the performances in the various skin activities were plotted against each other, it could be concluded that these personal care ingredients were specific in their skin efficacy, i.e. they may be good in one property but poor in another. Figure 2 shows that the emollients could be subdivided in two groups, one group of ingredients with a low elasticity performance but a wide range of moisturization performances and another category of emollients with a low moisturization performance but a wide range of elasticity performances. Subsequent work in which combinations of low- and high-performing moisturizing emollients were incorporated in formulations indicated that the efficacy of the formulation changed linearly as a function of the concentration of high-performing emollient, provided a certain threshold value had been reached (see Figure 3). The same could be observed for elasticity and substantivity. Relative Performance (%) 120 100 40 =o ili1111111111111111111111 o Figure I Moisturization performance of non-formulated personal care ingredients six hours drier application relative to untreated (0%) and glycerine-treated skin (100%), Unfortunately, it was not possible to measure the relative efficacy performance of pure emulsifiers in the same way as we tested the emollients as they cannot be applied to the skin in an undiluted form. When you formulate them, the other ingredients are likely to contribute to the skin performance as well. We therefore used the previously tested formulation series as the base formulation for the emulsifier studies. Using only the low- and high-performing emollient containing formulations, we changed the emulsifier whilst keeping the rest of the formulations constant. All emulsifiers were used at realistic concentrations. In addition,

2000 ANNUAL SCIENTIFIC SEMINAR 331 glycerine was added to two emulsifier systems to investigate the addition effect that this important humectant could have on the skin efficacies studied. Experimental conditions were identical to the previous studies. 20 ao 6'o 8'o 4oo Relative Moisturising Performance (%) A 55 õ 5o iI. 35 • 3o I• 25 ß 120 0 ' 1 '0 ' 1 '5 ' 2•0 ' 2'5 Concent•etion high-performing moisturiser (%wlw) Figure 2 Relative elasticity performance of non-formulated personal care ingredients as function of their relative moisturization performance Figure 3 Relative moisturization performance of formulations as function of the concentration of high-performing moisturizers For all skin benefits, the most important contributor to the overall efficacy of the formulation was the performance of the emollient. Formulations containing the high-performing emollient (B) always demonstrated a higher skin efficacy than the formulations containing the low-performing emollient (A), independent of the nature of the emulsifier system (#1-9) (see Figure 4). This was in line with the previous formulation study as the relative performances of the selected low- and high-performing emollients were very different. Much more surprising was the fact that certain emulsifiers were capable of improving the skin efficacy of formulations, regardless whether low- or high-performing emollients were used. This was independent of the skin efficacy studied, meaning that the emollient efficacy enhancing (EEE) effect of the emulsifier (system) was independent of the type of efficacy studied. Within the range of emulsifier systems studied, the w/o-emulsifier systems had both the highest and the lowest EEE. It can therefore not be attributed to the type of emulsifier. The addition of glycerine to formulations was only useful for those systems where either the emollient or the emulsifier or both were not optimal for delivering the skin efficacy. However, in formulations already containing the optimal combination of emollient and emulsifier, glycerine did not exert any further benefit for any of the skin efficacies studied. These studies showed that the emollient decides which skin efficacy a formulation may have, but that the extent of the efficacy is determined by the combination of emollient and emulsifier. M oisturisation Figure 4 Moisturization performance of eighteen moisturising formulations tested after a 6 hours application time, relative to untreated skin (0%) and glycerine-treated skin (100%). Formulation