4 Betty Croshaw Nowadays, reputable manufacturers exercise a microbiological quality control pro- gramme to ensure that they do not market a product that is a spoilage or health risk. Recalls and loss of large batches of materials place a heavy economic burden on the manufacturer. The need to include a preservative, or a mixture of preservatives, in order to prevent microbial spoilage or contamination of susceptible cosmetics and toiletries is also now universally accepted. The alternative of manufacturing these products in a sterile form in single-use containers would greatly increase their cost and is unjustifiable since a safe product can be prepared by a combination of good manufacturing hygiene and the inclusion of a suitable preservative system. FUNCTIONS OF PRESERVATIVES Preservatives are chemical agents that prevent microbial growth in a product, rendering it safe and increasing its shelf life. Some workers would agree that a static action was all that was required of a preservative. Tenenbaum (10) suggested that the preservative ability of a product should be in excess of the minimum necessary to inhibit expected flora. He recommended that an ideal preservative system should be 'self-sterilizing'. By the latter phrase, it is presumed he meant lethal to vegetative cells. A preservative should never be used to replace good manufacturing hygiene with continuous control of raw materials, especially water. The preservative is an aid in good manufacturing hygiene to combat unavoidable contaminants introduced in raw materials, from the equipment and containers used and from the operatives and the environment. Its main function is to prevent in use contamination by the consumer and to prolong the shelf life of the product. Ideally the preservative should be capable of eradicating high numbers of vegetative bacteria in case good manufacturing hygiene breaks down. Any cosmetic or toiletry must be free from pathogens even in small numbers. With the exception of eye cosmetics and baby products cosmetics and toiletries need not be free from non-pathogenic bacteria and fungi provided they are there in low numbers and in a static state. It must, however, be remembered that the line between pathogens and non-pathogens is a very tenuous one varying with different individuals, age-groups and state of health many organisms may be pathogens in the right environment. It is the function of the preservative to prevent contaminating organisms from multiplying and, ideally, it will eventually cause their death. Low numbers of non-pathogenic spores are probably harmless but the preservative must prevent the germination of these spores. The type of in-use contamination depends to a large extent on the presentation. Products supplied in tubes are less likely to become contaminated by the consumer than those supplied in jars. Some eye cosmetics incorporating applicators may be particularly hazardous unless adequately preserved since organisms from the skin are transferred to the preparation. The effective preservative should be capable of preventing the multi- plication'of any organism introduced during use whether this organism is a pathogen or a normal skin resident. Studies of the micro flora of selected areas of skin (e.g. McCon- ville and Anderson (11) on the outer eye) will help the microbiologist in consideration of in-use contamination. SELECTION OF A PRESERVATIVE SYSTEM There is still no satisfactory way of choosing a preservative system for a particular formulation on a theoretical basis. Nor can one from the many published lists

Preservatives for cosmetics and toiletries 5 ./1:1(12, 13, 14, 15) of available preservatives be merely chosen. In fact to the uninitiated these lists can be misleading since some of the agents may not be effective as preservatives •' 'because of their limited antimicrobial spectrum. Examples of these are the quatern- ary ammonium compounds, trichlorocarbanilide, the halogenated salicylanilides and bromochlorophen, all of which are potent antimicrobials as active agents for preparations 'such as soaps and scrubs where activity against Gram-positive bacteria and substan- tivity to the skin are the prime considerations. They are not effective preservatives. Every formulation must be considered on an individual basis although some general rules apply (3). The development of a new cosmetic or toiletry formulation involves consideration and adequate testing of the preservative system at an early stage and the formulatots and the microbiologist should work in close collaboration. The ideal preserva- tive does not exist and no one preservative system is satisfactory under all conditions. It may be that a combination of preservatives has to be used to obtain the desired effect in a particular formulation. The selection of a preservative depends on many factors 05) important considerations are the physical and chemical nature of the product, its potential use (e.g. on normal or broken skin, on infants, around the eyes), the type of container and the desired shelf life. All too frequently the final formulation can only be achieved on the basis of com- .'i:i.i promise safety, compatibility and efficacy are the most important factors influencing the preservative system. As Parker (16) points out although it is essential that the preservative capacity of a cosmetic is adequate to combat spoilage and in-use con- tamination it should not bestow the character of an antiseptic on the preparation. Many dermatologists regard the preservative as a necessary evil. Tronnier (17) makes the plea :. that cosmetic preservative levels should not be such as to upset the equilibrium of the biozone created by the microflora of the skin. The search for new preservatives continues and new ones appear but no single example has yet matched up to the ideal. It has been suggested that it is perhaps unrealistic to expect any compound to possess all the properties attributed to the ideal preservative (3) this belief is supported by the author. PROPERTIES OF THE IDEAL PRESERVATIVE The properties of the ideal preservative have been listed by many workers (e.g. 3, 12, 18). The following factors must be taken into consideration. Antimicrobial activity Any preservative must have broad spectrum antimicrobial activity since Gram-negative and Gram-positive bacteria, fungi and yeasts may be involved as contaminants and/or spoilage agents. The use of a preservative with high activity against some organisms and much lower activity against others may lead to the selection of insensitive organisms. One of the major disadvantages in the use of 2, 4, 4'-trichloro-2'-hydroxydiphenyl ether (lrgasan DP 300) as a preservative is its Pseudomonas gap (19). Since pseudomonads are the most commonly encountered contaminants in aqueous products their importance cannot be overlooked (10, 20). They can render conditions suitable for less adaptable spoilage organisms for example they can create conditions favouring the growth of anaerobes (2).