j. Soc. Cosmetic Chemists 16 395-403 (1965) ¸ 1965 Society of Cosmetic Chemists of Great Britain Hygiene in Manufacturing Plant and its Effect on the Preservation of Emulsions DOREEN L. WEDDERBURN* Presented at the Symposium on "Preservatives and Antioxidants", organized by the Pharmaceutical Society of Great Britain and the Society of Cosmetic Chemists of Great Britain, in London on I7th November 196d. Synopsis--Emulsions, which under normal circumstances are adequately preserved against microbial decomposition, can and often do break down when unusually large numbers of micro-organisms are accidentally introduced. The origins of excessive contamination frequently lie in the resin beds of demineralized water units, in filters, and in poorly designed plant which cannot be cleaned and sterilized effectively. Precautions can be taken to avoid circumstances in which bacteria and fungi can multiply in manufacturing plant, and the best ways of guarding against this are the elimination of "blind ends" and dead spaces in equipment, and meticulous attention to plant cleaning and sterilization. The washing of machinery with warm detergent solutions is often inadequate because residues of emulsion diluted with the wash-solution can provide a favourable environ- ment for rapid microbial growth in stagnation areas. Lessons in good plant design and hygienic practice can be learned from the food industry where good housekeeping is essential in the avoidance of spoilage. Modem pharmaceutical and cosmetic emulsions are more susceptible to microbial decomposition than they were in the past, because many new materials are biodegradable, and consequently more rigorous standards of cleanliness, and sterility are now needed in manufacture. In most well run factories, gross contamination of products by undesirable chemicals and frank dirt is usually avoided because such contamination is readily detected during routine testing and quality control. The unseen contamination by unusually large numbers of bacteria or fungi, which can occur from time to time, however, is probably the biggest enemy in a factory producing emulsions. Firstly, because *Unilever Research Laboratory, Isleworth, Middlesex. 395

396 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS routine testing may not include microbial assay, and secondly even if it does, the examination of small batch samples may fail to reveal the potential dangers. Emulsions designed for topical application to the skin such as cosmetic creams and lotions need not, of course, be completely free from non- pathogenic bacteria and fungi, but the few organisms present in any product at the time of manufacture must be prevented from multiplying during the product's shelf and user life by an effective preservative. In general, preservatives are included in these products at a low concentration which is only sufficient to hold moderate numbers of organisms in a quiescent state, and an increase in preservative concentration is often undesirable because of increased cost and, perhaps more important, the increased risk of toxicity to the skin and mucous membranes. If, by any chance, unusually large numbers of organisms are introduced into a product during manufacture or packaging, a preservative which is normally perfectly adequate may be overcome with the result that the product is virtually unprotected against microbial spoilage. In these circumstances, the emulsion may break down because the emulsifier has been metabolized, off-odours may develop as a result of utilization of various constituents, gas may be produced, discolouration may occur if pigmenting bacteria are responsible, and perhaps worst of all because of its visibility to the customer, fungal growth may occur on the surface of the product and inside the pack. There are no hard and fast rules about the "best" types of preservatives for use in emulsions nor about the concentrations at which they should be used since all emulsions differ in their physical characteristics, and in the nature and concentration of their constituents. Some constituents will restrict microbial activity, while others will provide nourishment for growth some may be grossly contaminated themselves. The pH of the product may favour or discourage growth of some organisms, and the ratio of water to oil will also influence the likelihood of the survival and multiplication of micro-organisms. For all these reasons, a preservative must be selected on the basis of its suitability for one particular system, and not because it has proved effective in other systems. Suggestions about the preservation of emulsions are given by Wedderburn (1). Once a compatible and effective preservative has been selected, however, steps must be taken to ensure that it does not fail in the occasional batch of product when manufacturing conditions are not all that they should be.