FUNCTIONAL PROPERTIES OF GLYCERIN 235 it can impart to formulations. Approaches to mitigate this negative frequently involve the use of specialty hydrophobic powders such as aluminum starch octenylsuccinate (15). I personally know of a specific example whereby an efficacious, prototype formulation containing 25% glycerol was made commercially viable when this starch derivative was introduced in the early 1970s. The inclusion of about 5% of the above-mentioned hydrophobic starch significantly improved application properties and sensory character- istics of the skin cream. I have also learned from a respected cosmetic industry consultant that the inclusion of branched chain esters in emulsion systems also serves to improve the application properties of formulations with high glycerin levels. In the publication by Shapiro (12), he states that the performance of high-glycerin formulas was in part due to their unique formulations--"that is, emulsification systems which create an HLB balance that facilitates highly efficient delivery of glycerin into the stratum corneum." A recent patent issued to Epstein (16) for an oil-in-water skin care composition em- ploying an emulsifier such as dimethyl distearyl ammonium halide with a substantially nonionizable humectant, such as glycerin, and a weakly acidic material, such as glycolic or lactic acid, was claimed to provide superior moisturization properties. A therapeutic- type commercial skin-moisturizing lotion (17) utilizing dimethyl distearyl ammonium chloride in a vehicle with high glycerin content exhibits, in my judgment, good sensory and application properties. The formulation, shown in Table V, for a prototype cationic lotion containing 8% glycerin is claimed by the raw material supplier (18) to have exceptional application properties, from rub-in to dry-down. This type emulsion vehicle may be suitable to hold even higher levels of glycerin, while maintaining acceptable application properties and cosmetic esthetics. A study by Fluhr eta/. (19) has demonstrated that glycerol is capable of enhancing the skin hydrating properties of water-in-oil emulsions. In addition, they have found that a combination of 5% glycerin and 5% urea in either w/o or o/w emulsions has hydrating Table V Formulation for a Prototype Cationic Lotion Containing 8% Glycerin Part A Behentrimonium methosulfate (and) cetearyl alcohol 1.17 Emulsifying wax NF 1.00 Stearyl alcohol NF 0.33 PPG-2 myristyl ether propionate 1.00 Pentaerythrityl tetracaprylate/caprate 0.67 Mineral oil 1.00 Petrolatum 2.00 Dimethicone 350 cs 0.50 Part B Deionized water 82.33 Glycerin 8.00 Part C Hydrolyzed whole wheat protein 1.00 Propylene glycol (and) diazolidinyl urea (and) methylparaben (and) propylparaben 1.00 100.00%

236 JOURNAL OF COSMETIC SCIENCE and protective properties on the stratum corneum functions. This combination was found to be more effective than either 10% urea and slightly more effective than 10% glycerin. It is possible that urea enhances the penetration of glycerin into deeper layers of the stratum corneum and thus improves the function of glycerin. In a study by Sagiv et aL (20) entitled "The efficacy of humectants as skin moisturizers in the presence of oil," the researchers found that treatments with glycerol (1 M) in water reversed skin dryness as measured by a corneometer and mexameter (measurement of erythema). When glycerol dissolved in medium-chain triglycerides was tested, no mois- turizing effect was found. This study confirms previous findings that glycerol requires an optimum concentration of water to function effectively. CONCLUSION As indicated above, the selection of emulsifying agents and the choice of vehicle addi- tives have the potential to influence the functionality of glycerol. Much remains to be studied systematically in these areas. I expect that future studies with glycerol formu- lations will include the use of liquid crystal, polymeric, and dimethicone copolyol emulsifier systems. The inclusion of appropriate skin barrier agents, such as petrolatum and or polymeric agents, is anticipated to further augment skin hydration and the protective properties of formulations containing glycerin. Glycerol presents a wonderful example of how recent basic scientific advances, combined with diverse bioengineering technology and sophisticated clinical testing methodolo- gies, have enabled us to gain a new appreciation for a classical cosmetic raw material with recently discovered multiple mechanisms of action. REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) Glycerine, a Key Cosmetic Ingredient (Marcel Dekker, New York, 1991), p. 1. Skin protectant drug products for over-the-counter human use, Federal Register (tentative), February 15, 1983. Ajinomoto Bulletin PRD-8101. V. Deshpande, Cosmet. Technol., September 1980. D. R. Highley,•l. Soc. Cosmet. Chem., 27, 351-363 (August 1976). D. L. Bissett, J, Soc. Cosmetic Chem., 35,345-350 (November 1984). M.D. Batt, J. Soc. Cosmetic Chem., 39, 367-381 (November/December 1988). C. L. Froebe, J. Soc. Cosmetic Chem., 41, 51-65 (January/February 1990). S. E. Friberg,J. Disp. Sci. TechnoL, 6, 485-495 (1985). S. E. Friberg,J. Soc. Cosmet. Chem., 41, 155-171 (May/June 1990). A. Rawlings, Arch Dermatol. Res., 287, 457-464 (1995). W. R. Shapiro, Cosmet. Dermatol. (November 1996) (Supplement: Proc. First Int. Symp. Cosmet. Efficacy, April 1996, 26-30). J. W. Fluhr et al., Acta Derre. Venereol., 418-421 (1999). M. Denda et al., JID, III, 5 (November 1998). Dry-Flo, technical literature, National Starch. U.S. Patent 6,017,548, assigned to the Andrew Jergens Company. Curel Extreme Care Body Lotion, technical literature, the Andrew Jergens Company. Croda Formula SC-192-1-Low Solids Cationic Lotion, technical literature. J. W. Fluhr, G. Vrzak, M. Gloor, Z. Hautkr., 73, 210-214, 1998. A. E. Sagiv et al., Skin Res, Technol., 7, 32-35 (2001).