j. Soc. Cosmet. Chem., 36, 255-269 (July/August 1985) Factors in the occlusivity of aqueous emulsions. Influence of humectants T. H. CHOUDHURY, J. P. MARTY, A. M. ORECCHIONI, M. SEILLER, and J. WEPIERRE, Laboratoire de Pharmacologie and Laboratoire de Pharmacie Galdnique, Facultd de Pharmacie, Universitg Paris-Sud, F.92290, Ch•itenay-Malabry, France. Received July 30, 1984. Synopsis In this work, factors controlling occlusivity of emulsions when humectants are added were studied. Emulsions were prepared from perhydrosqualene (P.H.S.) and mineral oil using ester and ether non-ionic surfactants having various HLB values in the presence of sodium 5-pyrrolidone-2-carboxylate, sodium lactate, and urea each at concentrations of 0, 0.62, 1.25, 2.5, 3.75, and 5%. Physicochemical parameters analyzed included isotropic oily phase formation capacity, viscosity, conductivity, and microscopy of the oil-surfactant-humectant residual films after application. Occlusivities of emulsions and residual films were determined using a highly hydrated gelatin model. Addition of humectants in the emulsions induced variable effects on occlusivity which was increased, decreased, or not modified. Nevertheless the modifications of the occlusivities of emulsions in the presence of humectants were related to simultaneous variations of their isotropic oily phase formation capacities. Viscosity and conductivity did not correlate with the occlusive properties of emulsions. Microscopic study proved that the isotropic oily phase leaves a continuous film on the application surface. Thus, the emulsions made with emulsifiers having HLB values, which facilitated the formation of an isotropic oily phase in various conditions of relative humidity, provided a more continuous film and thereby manifest the greatest occlusivity. INTRODUCTION A water level of less than 15 % in stratum corneum can render the skin dry and chapped (1-3). Moisture loss of human skin through evaporation can be reduced by using emulsions of varying degrees of occlusivity (4,5), mainly prepared from petrolatum, lanolin, beeswax, and various lipophilic phases (oils) which are known to act as occlusive moisturizers. Water in oil (W/O) emulsions are considered more occlusive than oil in water (O/W) emulsions (4,6). Handjani-Vila et al. (7) have suggested that the moisturizing effect of W/O emulsions is related to regulation of water loss by the specific nature of emulsifiers permitting a lamellar organization of lipids and not to the occlusivity of oily components. As shown before (8), all emulsions regardless of their type (O/W or W/O) lose more than 90% 255

256 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of their water content within 15 minutes of application. What remains is the residual non-volatile parts consisting of lipophile phase, surfactant, and a small amount of water. These have the ability to form an isotropic oily phase. This mainly depends on the HLB value of the surfactant. Thus, occlusive properties of emulsions have already been shown to be related to the capacity of their non-volatile parts to form an isotropic oily phase. The occlusivity of emulsions also depends on the initial occlusivity of the oily phase. Occlusivity increases with the amount of oil phase and decreases with the amount of surfactant. In a previous study of a large number of emulsions (8), especially O/W types, the occlusivity was found greatest at the HLB value which allowed the formation of the largest surface area of isotropic oily phase in a ternary diagram: water-surfactant-oil. A relationship between the occlusivity of emulsions and the formation of an isotropic oily phase was thus established. The above relationship was complicated in the presence of humectants used at 2.5 and 5% (t0). Their influence on the occlusivity of emulsions was surprisingly variable depending on the nature of the oil, surfactant, humectant and the HLB value. The change in occlusivity did not correspond to the variations of the surface area in the phase diagram of the isotropic oily phase. As a matter of fact, the concentrations of humectants in the residual films of emulsions after application are greater (10 to 20%) than in the isotropic oily phase determined in our experiments and consisting of oil, surfactant, and a 2.5 or 5% aqueous solutions of humectants. The objective of this work is to clarify the relationship between the occlusivities of emulsions containing humectants, the isotropic oily phase (being more accurately mea- sured), and other physical factors. The approach is to study a selected number of emulsions prepared from perhydro- squalene or mineral oil using ester or ether type surfactants in the presence of various humectants and to analyze the following physicochemical parameters: ß occlusivities of emulsions and of their non-volatile parts. ß capacities of emulsions to form an isotropic oily phase. ß viscosities of non-volatile parts of emulsions. ß conductivities of emulsions and of their non-volatile parts. ß occlusivities of isotropic ternary mixtures corresponding to the non-volatile parts of emulsions. ß microscopy of residual "films" of emulsions after application in usual conditions. The choice of emulsions and humectants was made considering the facts (t0) that in some cases the occlusivity decreases or remains unchanged at certain HLB values of surfactants, and increases or decreases depending on the nature of oil and surfactant. EXPERIMENTAL PROCEDURE MATERIALS Lipophile phases: Perhydrosqualene (P.H.S.) • and mineral oil 2 were as described in Pharmacop6e Frangaise IX. • Laserson et Sabetay, 14 rue Jean Bonal, F. 92250 La Garenne. 2 Mayoline 238 Cra Esso, 6 avenue Gambetta, 92420 Courbevoie.