J. Soc. Cosmet. Chem. 28 3-16 (1977) ¸ 1977 Society of Cosmetic Chemists of Great Brita#• Preservatives for cosmetics and toiletries Presented on 23 February 1976 at the Symposium on Microbiological Safety in Cosmetic and Toilet products, Birmingham BETTY CR O S HAW The Boots Co. Ltd, Research Department, Microbiology, Nottingham. Synopsis The need for preservation of cosmetics and toiletties and the function and selection of a satisfactory preservative system are discussed. The properties of the ideal preservative are considered and the properties of some of the newer preservatives described. Introduction It has been known for many years that some cosmetics and toiletries will support the growth of microorganisms (1) and that microbial action may cause spoilage problems (2) exemplified by visible growth or by chemical changes in the product. These changes may manifest themselves in a number of ways, e.g. by hydrolysis, oxidation, reduction causing off-odours, change in colour, adverse changes in pH, breakdown of the emulsion or change in texture of the product (2, 3, 4). More recently the introduction of new ingredients such as proteins, gums, vitamins, herbs, beer, some of which may be merely 'promotional additives' (5), has increased the microbiological hazard. The widespread use over the last two decades of nonionic surfactants to replace anionic emulsifiers has resulted in superior and more stable cosmetics but this change has also increased the risk of microbial contamination since many of these nonionic surfactants will support the growth of Gram-negative bacteria and particularly pseudomonads (6). Bryce and Smart (7) found that contaminated shampoos invariably contained Gram-negative organisms and their survey coincided with the change from anionic to nonionic surfactants. The degree of microbiological risk is affected by the physical state of the product. Aqueous solutions and oil-in-water emulsions are highly susceptible to microbial con- tamination. Water-in-oil emulsions are less susceptible because the continuous oil phase acts as a barrier to the penetration of microorganisms into the water phase and also impedes the spread of growth through the system (8). If, however, such a formulation is unstable and separation occurs, the separated aqueous phase is very vulnerable. Water-in-oil emulsions although less susceptible to microbial contamination are generally more difficult to preserve. Water, the raw material common to many cosmetics and toiletries, may often be the prime source of contamination. The most frequently reported contaminants in recent years have belonged to such genera as Pseudomonas, Klebsiella, Achromobacter and /llcaligenes. These bacteria are common residents in water and it is now widely believed that the water used in the preparation of toiletry products is their likely source (9). A consumer is unlikely to use a spoiled product but he or she could unknowingly use a contaminated cosmetic or toiletry. The possible health hazard is readily apparent since these products may be used on infants, by the old and the sick and by hospital staff and patients.

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