HYGIENIC MANUFACTURE AND PRESERVATION 777 aceous product, •vhich increases with time and is accelerated by elevated temperatures. 4.3t33 Uses For preservation of emulsions, liquid soap and some proteinaceous cosmetic systems, Dioxin may be used at a level of about 0.1%. 4.37 Phenols Phenolic compounds in general interact to form complexes with poly- vinylpyrrolidone and certain glycols such as polyethylene glycol 13 000 or polypropylene glycol 1 200, resulting in precipitation or separation of oil, and loss of antimicrobial activity. These compounds have a high oil:water partition coefficient and are usually more active in acid than in alkaline conditions they are unstable to light, sometimes causing product dis- coloration. Although many of these compounds are too irritant for use as preservatives in cosmetics, the halogenated phenols in particular have been employed for this purpose. Thus, p-chlor-m-cresol, p-chlor-m-xylenol, and dichlor-m-xylenol have been used in cosmetic preparations. o-Phenyl- phenol has been recommended for impregnation of paper liners for cosmetic jars. It should be borne in mind that the p-hydroxybenzoates are phenolic compounds, having similar physico-chemical properties to the phenols generally. 4.38 Quaternary ammonium compounds The use of these compounds in cosmetics is limited by the frequency of inactivation by other ingredients, especially nonionic and anionic sur- factants they also interfere with the stability of some cosmetic formulations. However, they are readily water-soluble and inhibit bacterial growth at high dilution. Benzalkonium chloride has been found useful at 0.1% con- centration. Whilst low concentrations of quaternary ammonium compounds appear to be quite safe to use, high concentrations are usually severe eye irritants. 4.3•) Alcohols Where appropriate, ethanol and isopropanol may be incorporated in liquid and other preparations in order to impart preservative activity. Concentrations of alcohol from 5-10ø//o upwards generally inhibit moulds and bacteria, and give useful protection against further microbial con- tamination.

778 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 4.4 New preservatives 4.41 Phenonip (Nipa Laboratories Ltd.) This is a proprietary preparation based on p-hydroxybenzoates. It is supplied in the form of a colourless solution miscible with water, claimed to be active against bacteria, yeasts and moulds. Phenonip is stable on storage, compatible with proteinaceous, anionic and cationic systems, and is stated to maintain its activity over a broad pH range. It is recommended by the manufacturers as a shampoo preservative at levels of 0.5-1.0%. Each formulation or composition, however, needs to be examined in- dividually and bacteriological control tests should be carried out. 4.42 Preservative mixtures The principle of blends of several preservatives has not been extensively explored. Dehydroacetic acid has been used with sorbic acid esters (2): studies on various cosmetic formulations containing nonionic surfactants have also indicated that combinations of sorbic acid and hexylene glycol may be effective preservatives (3). Other references to the beneficial use of synergistic combinations have been made (4-7). REFERENCES (1) "Eurotox" Report, J. Soc. Cosmet. Chem. •lI1 322 (1962). (2) Manowitz, M., in Lawrence, C. A. and Block, S.S. DisinfectionSsterilization and preser- vation 555 (1968) (Lea and Febiger, Philadelphia). (3) Barr, M. and Tice, L. F. J. Am. Pharm. Assoc. 46 455 (1957). (4) Myddleton, W. W. Mfg. Chem. 81 256 (1960). (5) Gershenfeld, L. Am. Perfumer Cosmetics 78 55 (October 1963). (6) Maccacaro, G. A. _Progress in industrial microbiology8 (1961) (Heywood & Co., London). (7) Boehm, E. E. J. Soc. Cosmet. Chem. 19 531 (1968)