Methylparaben (MP) Ethylparaben 99-76-6 120-47-8 • Acts by disrupting membrane transport processes • Inhibits protein synthesis (ATPases/ phosphotransferases) • Inhibits DNA and RNA synthesis • Causes leakage of cytoplasmic contents • Inhibits oxygen consumption of mitochondria in fungi 0.4% (acid) for a single ester 0.8% (acid) for a mixture of esters (12,17,29) Propylparaben (PP) Butylparaben 94-13-3 94-26-8 0.14% (acid) for the sum of the individual concentrations 0.8% (acid) for a mixture of methyl and ethylparaben, but not exceeding 0.14% Not to be used in leave-on products designed for application on the diaper area of children under three years of age Natural antimicrobial agents • Denatures membrane proteins • Inactivates enzymes • Destabilizes the proton motive force and electron flow • Mediates active transport and coagulation of the cell content • Causes breakdown of the permeability barrier • Inhibits the synthesis of DNA, RNA, proteins, and polysaccharides • Effects metabolic pathways and cell division (4,30–38) Phenoxyethanol (PE) 122-99-6 • Causes membrane damage, resulting in leakage of cytoplasmic constituents • Prevents cell growth by inhibiting DNA and RNA biosynthesis • Acts on energy metabolism through inhibition of malate dehydrogenase • Disrupts the proton gradient 1% Intended for leave-on products designed for application on the diaper area of children under three years of age (28,39– 43) Sorbic acid (SA) Potassium sorbate 110-44-1 246-376-1 • Acidifies the cytoplasm by the penetration of uncharged organic acids • Changes the fluidity of the plasma membrane 0.6% (acid) (44,45) a Maximum concentration according to Annex V of Regulation European Commission No. 1223/2009 or usual concentration for unregulated. 100 JOURNAL OF COSMETIC SCIENCE

101 PRESERVATION OF PERSONAL CARE AND COSMETIC PRODUCTS Clean beauty is having a moment, with an estimated global growth from US $5.4 billion in 2020 to US $11.6 billion by 2027, growing at a CAGR of 12.07% (13). The U.S. Food and Drug Administration (FDA) and other global institutions have failed to define clean which is sometimes confused with natural, leaving these labels open to interpretation by nondermatologist retailers, bloggers, and celebrities. Clean beauty products often claim to be safe, nontoxic, and has transparent labeling of ingredients. However, clean beauty is not necessarily natural and natural is not necessarily clean. The clean beauty and natural movements have demonized hundreds of compounds, while products with a clean or natural claim are not necessarily safer for consumers (14). Prior to COVID-19, natural consumers avoided ingredients such as preservatives and artificial ingredients in their beauty products due to perceived health risks. With more concern surrounding shelf stability and sanitation across consumer-packaged goods categories, consumers will be more willing to accept these ingredients as long as brands provide evidence of their efficacy and safety from both health and environmental perspectives. As consumers become more aware about viruses and germs living on surfaces, packaging for cosmetic and personal care products may change. Spray and stick formats in both cosmetics and facial skincare have been increasing in popularity, and with the arrival of COVID-19, “touchless” beauty products will see increased demand (15). ANTIMICROBIAL AGENTS BENZALKONIUM CHLORIDE (BAC) Since 1935 a quaternary ammonium compound, BAC, has been used as a preservative in medical preparations, cosmetics, and over the counter products. Benzethonium chloride and cetyl peridium chloride are part of the same chemical group. They act by adsorbing to the cytoplasmic membrane, thus causing leakage of the constituents. They are more active against Gram-positive bacteria. The activity against fungi, mycobacteria, and Gram- negative bacilli is comparatively weak (16,18). BAC is the most common primary active ingredient of non-alcohol-based hand sanitizer (46). The Cosmetic Ingredient Review (CIR) expert panel concluded that BAC may be safely used as an antimicrobial agent at concentrations up to 0.1%. Nevertheless, the panel noted that it might enhance the dermal penetration of other chemicals, thereby increasing the risk of sensitization and/or irritation (47). BENZOIC ACID (BEC) AND SORBIC ACID (SA) AND ITS SALTS Decreased use of traditional preservatives (e.g., parabens, isothiazolinones, formaldehyde releasers, and organic halogens) has boosted interest in alternative means of preservation with other antimicrobial choices, including organic acids such as BEC, SA and its salts (48). BEC and its salt, sodium benzoate (SB), are reported to function as fragrance ingredients, pesticides, pH adjusters, preservatives, and/or viscosity-decreasing agents in cosmetic products (49). In general, BEC and SB have the broadest spectra of antimicrobial activity and are useful against many spoilage bacteria, fungi, and yeasts. As preservatives are used in a wide range of cosmetic product types, they can be applied to the skin, nails, or hair and may come into contact with the eyes and mucous membranes (12,49,50). The