210 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS a5 Kupperman, H.S. A nat. Rec., 1944, 88, 442. a• Hamilton, J. B., and Hubert, G. Science, 1938, 88, 481. a? NicheIls, L. Lancet, 1946, g, 201. as Frost, D.V. Physiol. Rev., 1948, gS, 368-82. a9 Zarafonetis, C. J.D.J. invest. Derrn., 1950, 1õ, 399-401. 40 Keil, H. L., and Nelson, V. E. J. biol. Chern., 1931, 93, 49-57. 4• Gorter, F. J. Nature, Lend., 1935, 11•õ, 185. 4• Ire, M. Tohoku J. exper. Med., 1952, õõ (suppl. 1), 101. 49 Henschke, V., and Schulze, R. Strahlentherapie, 1939, {14, 14-42. 44 Blum, H.F. Physiol. Rev., 1945, gõ, 483-529. 45 Fitzpatrick, T. B. The Nature of Hair Pigments. 1957 Symposium on The Biology of Hair Growth, London. (To be published.) 4• Flesch, P., and Rothman, S. J. invest. Derrn., 1945, {1, 257-70. * Much of the material covered in this presentation has appeared in the chapter on Pigmentation by the author in: Rothman, S., Physiology and Biochemistry of the Skin, 1954, 515--63. (Chicago: The University of Chicago Press.) PRESERVATION OF TOILET PREPARATIONS CONTAINING NONIONICS DOREEN L. WEDDERBURN, B.Sc.* Based on • lecture delivered before the Society on 29th November 1957. The effect of nonionic materials on preservatives has been studied thirty-six nonionics and twenty-six preservatives were used in the investiga- tion. The nonionic surfactants reduced the efficiency of all the preservatives when the ratio of surfactant to preservative exceeded certain critical values, whereas non-surface-active nonionics did not. The critical ratio varies for each preservative and is dependent on the amount and type of nonionic sur- factant present. The possibility that certain nonionic surfactants protect micro-organisms, rendering them more resistant to preservatives, is also discussed. INTRODUCTION FOR MANY years soaps and anionic detergents have been used in toilet preparations as emulsifiers or on account of their cleansing properties. Preservatives were normally added to these products and adequate preserva- tion was not difficult. In recent years, nonionic surfactants have been increasingly used in toilet preparations, particularly as emulsifiers, solubil- isers and lather boosters. Because they have several advantages over anionic materials, nonionics are largely replacing the more conventional materials as emulsifiers in toilet preparations. As a result of using these materials the pH of products containing them is often lower than when soaps are used. Previously, almost all cosmetic creams were alkaline and did not provide environments particularly suited to the growth of micro-organisms, so that only mildly bacteriostatic or fungistatic preservatives were often adequate, but, when nonionics are * Unilever Ltd., Toilet Preparations Development Unit, Isleworth, Middlesex.

PRESERVATION OF TOILET PREPARATIONS CONTAINING NONIONICS 211 used, the pH is often between 5 and 7, and permits a more favourable growth environment. Now that so many toilet preparations are made to a pH that is nearly neutral or acid, more efficient preservatives are needed because bacteria and fungi can live and multiply more readily in nearly neutral conditions. The subject of this paper, however, is not the efficiency of preservatives at lower pH levels, as many function more effectively under acid conditions, but it deals with their effectiveness in the presence of nonionic materials. During the last few years there have been many references in the technical press concerning the effect of nonionics on germicides. In 1950, Bolle and Mirimanoff • reported that Tween 60, Tween 80, Span 20 and Arlacel 83 inactivated such germicides as Nipagin M, oxyquinolin sulphate and G-4, while Carbowax 1,500 did not. These assessments were made using fungi (penicillium and aspergillus) as the test organisms. Work along similar lines, again using fungi, was reported by de Navarre in 1956 and 1957.'•,• For many years nonionics have been used to stimulate growth in culture media, but little detailed work has been reported about the way in which they act on micro-organisms. It is known that because nonionics do not denature protein they do not inhibit the growth of micro-organisms (Glassman4). Dubos and Davies 5 have reported that Tween 80 encourages the growth of tubercle bacilli in culture media, and this they attribute to the surface activity of the nonionic. It is interesting to note that, for many years, tubercle bacilli, notoriously difficult to culture, have been grown successfully in egg yolk media. Egg yolk contains lecithin, which is a non- ionic surfactant. Engler 6 and Williams, et al.,7 have reported that nonionics stimulate the growth of certain micro-organisms. Several theories have been put forward concerning the physico-chemical mechanisms that might influence the inactivation of germicides by nonionics. Wurster and Rath 8 mention that complexes are formed between certain preservatives and Carbowaxes, while Arkins • states that organic preservatives are more soluble in the fatty part of certain compounds than in water and inactivation may be caused by this factor. Barr and Tice lø report that certain micro-organisms are capable of splitting the ester linkages of non- ionic surfactants of the fatty acid ester type, and have also commented on the failure of various phenolic preservatives to protect solutions of non- ionic surfactants from microbial attack. Higuschi and Lach" indicate that the hydrogen of the phenolic hydroxyl group in certain preservatives reacts with the basic oxygen in the ether group of polyethylene glycols, forming a complex. Hall and de Navarre" describe chromatographic evidence of the formation of complexes and indicate the possibility of hydrogen bonding. The activity of germicides is affected by several factors, for instance, proteins, both soluble and insoluble, have been known for many years to reduce their efficiency. Likewise, soap solutions markedly depress some