j. Soc. Cosmet. Chem., 46, 199-220 (July/August 1995) Cosmetic preservation DANIEL K. BRANNAN, Department of Biology, Abilene Christian University, Abilene, TX 79699. Received February I995. Synopsis The proper use of preservatives to prevent microbial contamination of cosmetics is often viewed as an art rather than a science. This view is a result of the multifactorial thinking that has to go into preservative selection. In this general article, an historical and critical review of preservative efficacy tests (PETs) is provided to understand the assumptions inherent in designing PETs. A conceptual framework of micro- organisms existing as communities in association with each other is also promoted, which provides a different understanding of how microorganisms contaminate cosmetics and why PETs are often misinter- preted. In addition, the mode of action of preservatives is discussed and contrasted with the mode of action of antibiotics. Finally, the role of the microbiologist is better defined in light of the fact that he or she must have expertise in far more than microbiology alone. INTRODUCTION Microbial contamination of cosmetics did not become an issue until about 50 years ago (1). The first microbial contamination observed was probably mold spoilage. Parabens provided adequate protection. During the 1960s, contamination of consumer products by Escherichia, Klebsiella, Enterobacter, Serratia, and Pseudomonas spp. occurred (2-5), demanding more effective and responsible preservation practices. By the mid-1970s, several cases of blindness due to Pseudomonas-contaminated mascaras caused eye cosmetics to be closely scrutinized (6-8). Most products reached the consumer in good microbi- ological condition, but they could not withstand contamination during use (9-14). The main issue addressed over the next few years was to develop preservative efficacy tests (PETs) that predicted the risk of consumer contamination. In 1975 and in 1985 the Food and Drug Administration (FDA) gave contracts to develop such PETs. The FDA never published the data from these studies, and no FDA •nethods were developed. In 1990, the Cosmetics, Toiletries and Fragrance Association (CTFA) published the results of a survey to determine if companies had already correlated their PET data with consumer use data (15). Nearly all the companies claimed they already had correlation programs in place, thus validating the ability of their company's PET to predict con- sumer contamination potential (16). Inherent in this validation process is the question, "What level of consumer abuse must a manufacturer anticipate for his product?" This question is usually answered with a legal definition: "To a level that is safe under 199

200 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ordinary use and foreseeable misuse conditions." Unfortunately, what constitutes fore- seeable misuse and ordinary use has never been defined. It is left up to the courts to decide when prosecuting specific cases. In the meantime, the company is left to decide for itself what "ordinary use and foreseeable misuse" really means. A joint program with the FDA, the CTFA, and the Association of Official Analytical Chemists (AOAC) was established to develop a standard PET in order "to demonstrate the ability of products to withstand microbial insult which may occur during intended use." However, the CTFA/AOAC/FDA collaborative study conducted no consumer use studies to correlate with PETs consequently, the collaborative study (publication ex- pected in 1996) was not validated by in-use testing. Two PET methods have been published with data allowing prediction of the in-use potential for consumer contam- ination (17-20). However, neither of these methods is available for replication since they both used challenge organisms unique to the investigators conducting the PET. THE IMPORTANCE OF PRESERVATION The cosmetics that most need preservatives are those that contain water. Products with low water activity (non-water based lipsticks, rouges, talcs, and antiperspirants) usually need little more than methyl or ethyl parabens to protect against fungi. Table I provides the water activity and pH limits for microorganisms and relates these to product types in general (21,22). The only limit to microbial life is the availability of liquid water, with microbes being found to grow at extremes of temperatures and pH (23,24). However, most organisms of concern to the cosmetic microbiologist are not extremo- Table I Water Activity and the Potential for Growth Problem organisms Examples of Water activity pH capable of growth cosmetic products 0.98-1.00 pH 5-9 Most Gram positives and negatives 0.95-0.97 pH 5-9 Most Gram positives and Liquid make-ups and eye area negatives (Pseudomonas begins products Below 5.5 0.92-0.95 Above 5.5 o. 90-0.92 Below 5.5 pH 5-9 0.80-0.90 pH 5-9 0.70-0.80 pH 5-9 0.65-0.70 pH 5-9 0.60-0.70 pH 5-9 Below 0.60 pH 5-9 to be limited) Some Gram negatives and most Gram positives (Pseudomonas limited) Few Gram negatives and most } Gram positives Most Gram positives Gram positive Lactobacilli and Staph. Staph., molds, yeasts Molds, yeasts Osmotolerant yeasts } Osmotolerant and xerophilic molds None Shampoos and emulsion products Some hair conditioners Some pressed powders Some rouges (non-water based) Lipsticks (non-water based) Some talcs Some antiperspirants