Géraldine Savary

Impact of emollients on the spreading properties of cosmetic products: a combined sensory and instrumental characterization.

This study deals with the impact of emollients on the spreading properties of cosmetic products using a combined sensory-instrumental approach. To that purpose, three esters and one silicone were selected and incorporated separately into an oil phase. Different cosmetic o/w emulsions were then prepared with these different oil phases. Both of them were analyzed by instrumental techniques and in vivo sensory analyses. A significant effect of the emollient used was established in emulsions and in oil phases as well. Concerning emulsions, results reveal a clear correlation between in vivo spreading evaluation and friction coefficient parameters measured by texture analyzer, despite a fairly low correlation coefficient (Pearson coefficient=-0.78). Concerning oil phases, characterization of spreading was done by monitoring the contact angle relaxation of a drop of solution after deposition on a flat PMMA surface whereas sensory procedure was based on spontaneous spreading of oil phases onto the skin. Finally, good correlations between in vivo sensory analysis and instrumental measurements of both oils and emulsions were found, thus promising the possible development of predictive tools to evaluate spreadability.

Cosmetics and Personal Care Products

Cosmetic and personal care products are complex mixtures intended to be applied to the external parts of the human body. In the long list of ingredients are included polymers which are either natural or synthetic. This chapter presents the main natural polymers used in cosmetics which are mainly polysaccharides and proteins obtained from vegetable, animal and biotechnology origins. The use of artificial polymers is discussed through the example of cellulose derivatives which are widely used for their physicochemical properties and cosmetic benefits. Natural polymers in cosmetics play many distinct roles; they can be chosen either to improve the stability of colloidal systems, to control the rheological properties from manufacturing to end-user or to achieve the sensory expectation and efficiency of the product during application. Natural polymers are thus multifunctional ingredients used in many different commodities sometimes alone, but more often in combination with synthetic polymers as illustrated through different examples including hair care, skin care or toothpaste products. Natural polymers own a growing place in the cosmetic field and this can be attributed to the ever increasing desire for “naturality”. Their applicability in this field is further enhanced by their processibility and the multiple options possible to control properties through their chemical modifications.

Stretching properties of xanthan and hydroxypropyl guar in aqueous solutions and in cosmetic emulsions

Filament stretchability of xanthan gum (XG) and hydroxypropyl guar (HPG) was investigated in aqueous solutions (0.125, 0.25, 0.5, 1, 1.2 and 1.5% w/w) and in O/W emulsions using a texture analyzer. Additionally, rheological characterizations were carried out on the systems and shear and oscillation parameters were used to interpret stretching properties. XG solutions exhibited a solid-like behavior with rheological parameters much higher than for HPG one whatever the concentration. Filament stretching values of XG solutions were superior to HPG for concentration below 1% w/w and then became comparable for higher concentrations. No meaningful relationship was found between rheological and stretching values. Synergy was observed for all XG/HPG mixtures at 0.125, 0.25 and 0.5% influencing both the rheological and the filament stretching values. The 25/75 XG/HPG ratio showed the maximum synergistic effect at all concentrations while the filament stretchability was enhanced in a wider range of ratios. XG and HPG did not present the same behavior in emulsions. No clear synergistic effect was observed and XG markedly influenced the emulsion filament stretching.

Interactions between UV filters and active substances in emulsion: Effect on microstructure, physicochemical and in-vivo properties

&NA; The objective of the present study was to develop, characterize and evaluate the clinical efficacy of topical formulations containing or not active substances and UV‐filters, separate and in combination. To this end a stable formulation was developed to which four aqueous active substances and four lipophilic UV‐filters were added. The formulations were then submitted to microscopic characterization by light microscopy, to particle size measurement, and to macroscopic characterization by rheology and texture analysis. Finally, a clinical efficacy study was conducted to determine the effect of the formulations on the skin after application for 1 h. The formulation containing UV‐filters showed a high polydisperse microstructure and a large amount of liquid crystals. The formulations containing active substances showed higher resistance to deformation, compression and penetration tests. Regarding spreadability, formulations containing UV filters alone or in combination with active substances showed higher resistance to spreading. This behavior was associated with greater clinical efficacy in terms of stratum corneum water content, protection of the skin barrier function and skin surface brightness. It was demonstrated that the efficacy of the formulation is mainly associated with its structure and the way it interacts with the skin surface. Finally, this study showed that the mixture of these ingredients for the development of multifunctional sunscreens improves the performance of the formulations.

Influence of the emollient on emulsions containing lamellar liquid crystals: from molecular organization towards applicative properties

The sensory perception of cosmetic emulsions is complex as it is governed by an important number of parameters like the choice of raw materials, their interactions, the structural organisation of the system, etc. The aim of the present work was to go further in the interpretation of the emollient‐surfactant interactions, towards the emulsions applicative properties. For this purpose, two systems containing liquid crystals of the lamellar type were formulated, differing only in the selected emollient.