MICROBIOLOGICAL SPOILAGE IN PHARMACEUTICALS AND COSMETICS 729 bacteria, Desulphovibrio or Desulphotomaculum species, which oxidize simple organic compounds and reduce sulphates to hydrogen sulphide. This then deposits iron sulphide due to the abundance of iron present in the environment where the oil is used. Emulsions O/w emulsions are particularly susceptible to spoilage as the water in the continuous phase allows contaminants to spread throughout the pro- duct. Preservatives generally exert their influence only within this phase, and at its boundaries, but their concentration depends on their relative solubilities in the particular oil and in water and on the oil water ratio in the emulsion (14). In addition to partition effects the activity of preservatives may be further diminished due to inactivation by compounds such as the nonionic emulgents. These possess little bactericidal adtivity and may even be utilized by pseudomonads (15, 16). In a comprehensive review Wedder- burn (17) pointed out that many other materials used in emulsions are susceptible to microbial degradation. Spoilage in emulsions can be manifest by changes in rheological proper- ties, including separation or 'breaking down'. Discolouration, decolouriza- tion, changes in odour and taste and signs of visible growth also occur. Creams and lotions A wide variety of complex cosmetic and toiletry preparations are included under this heading. Apart from the usual ingredients there is a current tendency to employ substances of natural origin including animal proteins and vitamins. These materials are not only highly nutrient to micro-organisms but may inactivate preservatives and even serve as a source of contamination. Glycerol is commonly used in both pharmaceutical and cosmetic formulations and may be metabolized by organisms frequently found in water. For instance, Klebsiella species will frequently produce gas in poorly preserved products when used to challenge creams and lotions containing this component. Mould growth is one of the most common causes of spoilage of creams of all types and can occur in products as varied as antifungal, calamine, baby and hair creams and a number of other cosmetic formulations including moisture and cleansing creams. The difficulties of preserving these products against mould growth are enhanced by the risk of contamination from containers, the presence of large air spaces and poor storage con- ditions.

730 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Ointments and oils As these are anhydrous materials, in theory they do not support the growth of micro-organisms. However, in practice they are often filled into jars or other containers with large air-spaces and this introduces the possibility of mould spoilage, as for creams, because these organisms can utilize atmospheric moisture. Whereas creams can supply moisture by evaporation, oils and ointments require the accidental ingress of water or the presence of a humid atmosphere. Fortunately a much smaller incidence of this kind of spoilage therefore occurs but we have seen a few examples of mould colonies on the surfaces of ointments, including white petroleum jelly, and ironically, fungicidal ointment. Oils are at a slightly greater risk than ointments as, being more fluid, they allow condensed water to carry organisms to the bottom of the con- tainer and remain trapped. Moulds have been reported to metabolize arachis oil and liquid paraffin (18, 19) and obnoxious odours, tastes and slimy deposits have been found in liquid paraffin while clumps of moulds, yeasts or bacteria have been seen in maize and olive oil. Without exception traces of water are found in these spoiled samples and the detection of foreign substances, such as food particles, often indicates the origin of the contamination. Shampoos Shampoos are particularly susceptible to contamination by a range of Gram-negative waterborne bacteria (20). Although they may support the growth of large numbers of bacteria without visible spoilage, slimy sedi- ments, pellicles, discolouration and odours are sometimes found and the loss of lathering properties has also been noted. Medicated shampoos are not immune from spoilage because the antimicrobial ingredients they contain often possess only a narrow spectrum of antimicrobial activity. It is almost impossible to keep shampoos away from the eyes of the user and con- tamination by invasive bateria such as pseudomonads must also render products of this type unfit for use, whether other spoilage has occurred or not. Syrups The sugar content of syrups inhibits the growth of many micro-organ- isms by virtue of its high osmotic pressure but osmotolerant moulds and yeasts are a source of trouble. Fermentation of the sugar by these organisms causes foul flavours due to the production of alcohol, lactic acid and other