THE EFFECT OF SORBIC ACID AND OTHER PRESERVATIVES ON ORGANISM GROWTH IN TYPICAL NONIONIC EMULSIFIED COMMERCIAL COSMETICS By R. DONALD CHARLES and PHYLLIS J. CARTER* Presented May 7, 1959, New York City OF THE MANY factors which determine the resistance of a cosmetic emulsion to organism growth, one has been distinguished by much attention in recent cosmetic and pharmaceutical technical literature--the effect of nonionic surface active agents on emulsion preservation. Most of the work published on investigations of this problem has been based upon studies of preservatives in laboratory culture media containing nonionic surfac- rants. The failure of many preservatives, especially the phenolic family, to arrest the growth of organisms introduced into this type of media has been attributed to the formation of a complex between preservative and surfactant which impairs the preservative's antimicrobial powers. Ex- trapolations of the results of this type of component evaluation into the field of cosmetic formulation have led some workers to what we believe are mis- leading conclusions. In this paper, we are presenting data which illustrate the need to consider the entire cosmetic formulation in dealing with the problem of preservation. Evidence for some sort of interaction between preservatives and nonionic materials with surface active properties is abundant in the technical litera- ture of the last ten years in the fields of cosmetics and pharmaceuticals. A review of this work, such as that recently compiled by Beckerr and Robin- son (1), is beyond the scope of this paper but it would be appropriate to mention in passing some of the more familiar investigators in this field, such as Fisher (2), Gershenfeld (3), Gregg and Zopf (4), Bolle and Mirimanoff (5), Hadgraft (6), Lawrence and Erlandson (7), deNavarre (8), Lord and Husa (9), Bart and Tice (10), Aalto, Firman and Riglet (11), Patel and Kostenbauder (12) and Wedderburn (13). The mechanism of the interaction between phenolic preservatives and nonionic emulsifiers has been explained by Higuchi and Lach (14) as the * Atlas Powder Co., Wilmington 99, Del. 383

384 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS formation of a hydrogen bond between the phenolic hydrogen and one of the ether oxygens of the polyoxyethylene chains which are found in many types of nonionic surfactants. Additional support for this explanation has been contributed by the work of Hall and deNavarre (1.5). The manner in which nonionic surfactant micelies could be solvated by hydrogen bonding and the way in which a phenolic molecule could be at- tracted to the surfactant micelie and held by a combination of hydrogen bonding and van der Waals forces has been discussed by Beckerr and Robin- son (1). Most of these studies have been concentrated on the detection of pre- servative-surfactant interaction in systems less complex than the cosmetic emulsions in which these ingredients are used. The demonstration of the effects of preservative complexing in these systems has been made on the basis of reduced activity of the preservative toward organisms introduced into a laboratory culture medium containing nonionic surfactants, or the proof of interaction has been based on physical measurements of dilute two and three component systems with water, such as dialysis studies (12) or turbidity determinations (16). Very little has appeared in the literature, however, in the way of documented correlations between the behavior of a preservative compound in a nonionic surfactant-nutrient broth combina- tion and the same preservative's behavior in a cosmetic emulsion. Lacking such a conversion factor, the other possibility of relating com- ponent testing to practice is the testing of the complete preserved formula- tion for resistance to organism growth. One of the few published examples of this type of work has been presented by Rdzols, Grundy, Kirchmeyer and Sylvester (17), who tested a group of pharmaceutical products by in- troducing a suspension of garden soil with its normal flora supplemented by the addition of the spores of nine molds. In the course of a study to determine the effectiveness of sorbic acid as a preservative for cosmetic emulsions based on nonionic surfactant systems, conducted for the Atlas Powder Company by Tice and Bart of the Phila- delphia College of Pharmacy and Science, we had occasion to have three typical cosmetic formulas tested for their resistance to organism growth. These formulas were o/w emulsions containing nonionic surfactant sys- tems and were first prepared with no preservative, then preserved with a widely used methyl parahydroxybenzoate/propyl parahydroxybenzoate combination and finally protected against organism growth with sorbic acid. Portions of the three modifications of each cosmetic preparation were then contaminated individually with six separate micro6rganisms, and the samples observed during a storage period of three months at room tempera- ture. Some of the results of this portion of the study alluded to in a paper pre-