107 PRESERVATION OF PERSONAL CARE AND COSMETIC PRODUCTS time are other factors affecting microbial resistance (12). Preservative resistance may be considered as the inactivation of the preservative agent, the reduction in preservative efficacy, or a tolerance of microorganisms (89). Generally, bacterial endospores (i.e., Bacillus and Clostridium) are the most resistant forms. In contrast, mycobacteria (due to cell wall composition) are more resistant than Gram-negative bacteria, while Gram-positive bacteria are most sensitive to preservatives (19). Microbiological contamination of cosmetic products is a matter of great importance to the industry and is potentially a major cause of both product and economic losses. The most common signs of microbial contamination are organoleptic alterations, (e.g., offensive odors), changes in viscosity, and color alterations (74). Moreover, in some cases, exposure to pathogenic microorganisms may cause human health problems (e.g., skin irritation, ACD, and infection, especially in the eyes, mouth, or wounds) (90,91). The different types of microorganisms vary in their response to antimicrobial agents and have different cellular structures, compositions, and physiologies. Traditionally, microbial susceptibility to antimicrobials has been classified based on these differences (92). The resistance of different types of bacteria (mycobacteria, nonsporulating bacteria, and bacterial spores) can be either a natural property of an organism (intrinsic) or acquired by mutation or acquisition of plasmids (self-replicating, extrachromosomal DNA) or transposons (chromosomal or plasmid integrating, transmissible DNA cassettes). Intrinsic resistance is demonstrated by Gram-negative bacteria, bacterial spores, mycobacteria, and, under certain conditions, staphylococci. Acquired, plasmid-mediated resistance is most widely associated with mercury compounds and other metallic salts. In recent years, acquired resistance to certain other types of biocides has been observed, notably in staphylococci (92,93). In comparison with bacteria, little is known about the ways in which fungi can circumvent the action of antimicrobial agents (94). There are two general mechanisms of resistance: (1) intrinsic resistance, a natural property or development of an organism, in which the cell wall presents a barrier to reduce or exclude the entry of an antimicrobial agent and (2) acquired resistance (95). Mold spores, although more resistant than nonsporulating bacteria, are less resistant than bacterial spores to antiseptics and disinfectants. The cell wall composition in molds may confer a high level of intrinsic resistance on these organisms (92). Some examples of mechanisms of microorganism resistance are organic acids (e.g., BEC), sorbic acid and its salts, which can be related to (1) degradation of the organic acid, sorbic acid may be degraded to 1,3-pentadiene by some species of Penicillium, and BEC is metabolized by several species of Pseudomonas and by Acinetobacter calcoaceticus (96) and (2) adaptation of the microorganisms to the acidic medium (the yeasts only adapt to small- chain fatty acids) may be achieved by using the H+-ATPase pump, by the accumulation of the anions to buffer acid pH, or by the synthesis of acid shock proteins (20). In the case of parabens, microorganisms are resistant due to (1) enzymatic inactivation after hydrolysis to 4-hydroxybenzoic acid by esterase (2) super expression of efflux pump genes and possibly (3) porin deficiency (97–99). The external membrane and lipopolysaccharides of Gram-negative bacteria can be responsible for the high intrinsic resistance to quaternary ammonium compounds (e.g., BAC). Pseudomonas aeruginosa modifies the outer membrane structure by changing its fatty acid composition and phospholipids, hindering the penetration of such antimicrobials (19,100). Microorganisms are very versatile and adaptive and, to survive, they need to be capable of dealing with toxic substances. There are multiple components in microbial cells that

108 JOURNAL OF COSMETIC SCIENCE may be targets of antimicrobial agents, and there are just as many targets that may be modified by microorganisms to enable resistance to those ingredients (93). Overexposure to preservatives can decrease the effectiveness of these ingredients, in addition to possible contribution to increased antimicrobial resistance. These problems can be reduced by conscious use of these ingredients by the cosmetic industry, accompanied by correct consumer use recommendations. CONCLUSION Attitudes and perception of cosmetic preservatives has changed significantly changed in recent years. Traditional safe preservatives (e.g., parabens) have been replaced by other ingredients of questionable safety. The use of antimicrobial alternatives and the “preservative-free” claim have become popular in the cosmetics market, due in part to current consumer beliefs that a product containing preservatives may pose a higher risk than “unpreserved” or “self-preserved” options. Unexpectedly, the COVID-19 pandemic paralyzed the global market, and cosmetic industries had to adapt to a new reality. Due to the widespread use of cosmetic products, the prevalence of allergies, microbiological resistance, the need for proper prevention of product contamination, and concerns over the safety of preservatives, further investigations into the modes of action of traditional or alternative preservatives are needed to create successful safety products. REFERENCES (1) E. Gerstell, S. Marchessou, J. Schmidt, and E. Spagnuolo, How COVID-19 is changing the world of beauty [Internet]. McKinsey &Company. 2020 [cited 2020 Jun 2]. Available from: https://www.mckinsey.com/ industries/consumer-packaged-goods/our-insights/how-covid-19-is-changing-the-world-of-beauty (2) R. Grabenhofer, Cosmetic trends and opportunities post-COVID-19 [Internet]. Cosmetics &Toiletries. 2021 [cited 2021 Mar 22]. Available from: https://www.cosmeticsandtoiletries.com/marketdata/ consumers/Cosmetic-Trends-and-Opportunities-Post-COVID-19-573961591.html (3) P. Mościcka, N. Chróst, R. Terlikowski, M. Przylipiak, K. Wołosik, and A. Przylipiak, Hygienic and cosmetic care habits in polish women during COVID-19 pandemic. J. Cosmet. Dermatol., 19(8), 1840– 1845 (2020). (4) A. Herman, Antimicrobial ingredients as preservative booster and components of self-preserving cosmetic products. Curr. Microbiol., 76(6), 744–54 (2019). (5) K. Ahuja and S. Singh, Cosmetic preservatives market size &share |statistics -2026 [Internet]. 2020. [cited 2021 Mar 10]. Available from: https://www.gminsights.com/industry-analysis/cosmetics- preservative-market. Global Market Insights, Inc. (6) E. Neza and M. Centini, Microbiologically contaminated and over-preserved cosmetic products according rapex 2008–2014. Cosmetics. 3(1), 3 (2016). (7) A. D. P. M. Canavez, G. de Oliveira Prado Corrêa, V. L. B. Isaac, D. C. Schuck, and M. Lorencini, Integrated approaches to testing and assessment as a tool for the hazard assessment and risk characterization of cosmetic preservatives. J. Appl Toxicol., 41(10), 1687–1699 (2021). (8) D.C. Steinberg, Frequency of preservative use update through 2014 [Internet]. Cosmetics &Toiletries. 2016 [cited 2020 Jan 29]. Available from: https://www.cosmeticsandtoiletries.com/regulatory/region/ northamerica/Frequency-of-Preservative-Use-Update-Through-2014-367684531.html. (9) A. F. Fransway, P. J. Fransway, D. V. Belsito, E. M. Warshaw, D. Sasseville, J. F. J. Fowler, J. G. DeKoven, M. D. Pratt, H. I. Maibach, J. S. Taylor, J. G. Marks, C. G. T. Mathias, V. A. DeLeo, J M. Zirwas, K. A. Zug, A. R. Atwater, J. Silverberg, and M. J. Reeder, Parabens. Dermatitis, 30(1), 3–31 (2019).