COSMETIC PRESERVATION 201 philes, and thus extremes of pH and A w can be used to control them. Where these extremes cannot be met, a biocide is used to control growth. Microorganisms metabolize product ingredients using a variety of hydrolytic enzymes to cause adverse changes in product odor, color, and viscosity. Even though health-related contamination incidences related to cosmetics are rare, a few have occurred and include infection from a hand lotion (3), eye infections from use of eye area cosmetics (25), and the death of one immunocompromised individual (26). Aside from spoilage prevention and health-related concerns, cosmetics also need to be adequately preserved to withstand consumer use. Manufacturing contamination can be controlled with good sanitation. But consumer use and abuse cannot be controlled. Consumers may repeatedly challenge the cosmetic with microorganisms. The bathroom, where most cosmetics and toiletry articles are used, provides heat and humidity needed for microbial growth (27,28). During use, cosmetics can be contaminated with a variety of spoilage organisms found in the household environment (29, 30). Table II lists some of the microorganisms that contaminate shampoos and skin lotions after consumer use (30). A few of these may invade and create disease (31). With more and more immunocompromised individuals in the population from the pandemic of AIDS, even spoilage organisms may be oppor- tunistic pathogens. The biggest contamination concerns are pathogens that present a frank health risk such as the pseudomonads (32). Cosmetics intended for eye area use are particularly suspect since the cornea, when compromised, is highly vulnerable to in- fection, and several instances of mascara contamination from Pseudomonas spp. have been reported (6-10). Thus, choosing the proper preservative and package is critical to providing appropriate protection to the product. Table II Types and Percentages of Microorganisms Contaminating Cosmetics After Use (30) Organisms Isolated from shampoo Isolated from skin lotion C itrobacter freundii 18 0 Enterobacter spp a 37 9 Klebsiella spp. b 9 9 Pseudomonas spp. c 9 21 Serratia spp. d 18 4 GNR e (nonfermentative) 0 4 GNR (fermentative) 9 0 CDC serotype IVC2 0 4 Bacillus spp. 0 4 S taphylococcus epidermidis 0 4 Propionibacterium sp. 0 4 Sarcina sp. 0 4 Diphtheroid 0 4 Yeasts and molds 0 29 • E. aerogenes, E. agglomerans, and E. cloacae. b K. pneumoniae and K. oxytoca. c p. putida, P. fluorescens, P. paucimobilis, P. aeruginosa, and P. maltophilia. • S. liquefaciens, S. odorifera, and S. rubidaea. e GNR, Gram-negative rod. Table adapted from Brannan and Dille (30).

202 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS However, selection of preservatives for a cosmetic is complex. The ideal characteristics of a biocide are that it be safe, stable, and compatible with both the product and the container, be inexpensive, readily available, approved by appropriate regulatory agen- cies, have a positive consumer perception, and be environmentally friendly. Raw ma- terial quality, container and cap design, expected shelf life and exposure conditions, and even how the consumer will use and misuse the product are additional considerations in choosing the preservative system (30,33). Compatibility of the biocide with other ingredients in the product requires the micro- biologist to have knowledge of the art of formulation. Suspended solids in a formulation (e.g., carbonates, silicates, talc, metal oxides, cellulose, and starch) may adsorb pre- servatives (34). Minor pH changes inactivate other preservatives (35-37). Minor shifts in ionic strength or changes in the buffering system in a product can also alter a bacterium's susceptibility to a biocide or affect how a preservative partitions between the water matrix and the microbial cell (38,39). Parabens provide unique formulation challenges for water-in-oil emulsions because they have an affinity for the oil phase while the microbes live in the water phase (40). Even the surfactant system used can affect biocide performance (41-43). In fact, nonionic surfactants are used to neutralize some preservatives (44-46). However, these same surfactants enhance quaternary ammonium compounds (47). Finally, protein (often used in conditioner and lotions) may also reduce the antimicrobial activity of many preservatives (48-50) the presence of hydrophilic polymers will affect others (51). Even simply choosing a container requires a microbiologist to check compatibility with the preservative (52,53). The preservative may either be absorbed into the container material in the case of lipid-soluble preservatives, inactivated because of complexation of the preservative with the dyes used in the plastic, or lost because of the volatility of the preservative (e.g., phenoxyethanol, formaldehyde, and ethanol). When considering containers, one should also not overlook the impact that dispensing closures have in preventing microbial contamination, especially during consumer use. Some closures provide more protection of products than others (30). Alternatively, some closures may inactivate the preservative (54). PRESERVATIVE EFFICACY TESTING DEFINING THE PURPOSE OF THE PET Test protocols for determining preservation efficacy in cosmetics vary (55-58). The logic and arguments that go into establishing these protocols are primarily based on consen- sus. These compendial efforts, such as those developed by the CTFA, are "state-of-the- art," but they are not rigidly controlled protocols subjected to multiple laboratory replication and statistical analysis. Nevertheless, they have been useful. The CTFA/ AOAC/FDA collaborative program mentioned previously may fill this gap despite not being a method that has been validated to predict consumer contamination potential. To develop such predictive tests, a company must employ a microbiologist who conducts a validated "in-house protocol" that is specific for the company's products. Alterna- tively, the protocol developed by the company may be contracted out to laboratories capable of conducting PETs.