cosmetics Article Why Are Wet Wipes So Difficult to Preserve? Understanding the Intrinsic Causes Paul Salama *, Ariel Gliksberg, Matan Cohen, Inbal Tzafrir and Noa Ziklo   Citation: Salama, P.; Gliksberg, A.; Cohen, M.; Tzafrir, I.; Ziklo, N. Why Are Wet Wipes So Difficult to Preserve? Understanding the Intrinsic Causes. Cosmetics 2021, 8, 73. https://doi.org/10.3390/ cosmetics8030073 Academic Editor: Enzo Berardesca Received: 27 June 2021 Accepted: 12 August 2021 Published: 16 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Innovation Group, Sharon Laboratories Ltd., Odem St. Industrial Zone Ad-Halom, Ashdod 7898800, Israel; Ariel@sharon-labs.co.il (A.G.); Matan.cohen.che@gmail.com (M.C.); Inbali@sharon-labs.co.il (I.T.); noa.ziklo@sharon-labs.co.il (N.Z.) * Correspondence: paul@sharon-labs.co.il; Tel.: +97-25-4216-6476 Abstract: Over the last two decades, significant advances have been made in developing disposable baby wet wipes. Wet wipes consist of two main components: nonwoven fabric and liquid. Being more than 90% water, wet wipes are more susceptible to microbial growth than typical personal care products; hence, high concentrations of preservative compounds are often used to ensure extended protection against contamination. However, there is an obvious tendency to minimize the concentration of irritating actives. Baby wet wipes should contain particularly mild surfactants, well- tolerated preservatives, and a buffer system maintaining the formulation pH at a suitable level for the infant’s skin. Efforts have been centered on removing ingredients with irritation potential, such as phenoxyethanol. In addition, a move towards more natural fabrics is occurring. However, these modifications provoke new challenges in preserving the final products. The nature and composition of the fiber can influence the interactions between the preservative and the wipe, subsequently affecting the performance of the preservative system. In this study, we analyzed the causes of the challenge in preserving wet wipes. We found that fabrics containing natural fibers are the main source of contamination, promoting the generation of biofilms on their surfaces. Moreover, the hydrophilic–lipophilic balance (HLB) was utilized to rationalize the physicochemical interactions between the fabric and the preservatives. Keywords: wet wipes; preservation; biofilm; hydrophilic–lipophilic balance 1. Introduction Wet wipes were originally developed as personal care products, yet with time they have become an increasingly popular item for everyday use in homes. Generally, wet wipes consist of two main parts: a nonwoven fabric carrier (wipe) and liquid. The wipes hold and spread the liquid or collect and hold dirt or other matters to be removed. The liquid impregnating the wipes is mostly water but also contains surfactants, a buffer, and preservatives. Nonwoven fabrics are broadly defined as sheet or web structures bonded together mechanically, thermally, or chemically by entangling fibers or filaments [1]. The fibers used to produce the wipe may be natural, such as wood pulp, or synthetic, such as polypropylene, polyester (PET), or combinations thereof. Low-cost synthetic fibers are the major raw materials of wet wipes, while natural fibers including wood pulp, viscose (a regenerated cellulose product), and cotton may be used for fine-tuning the desired features of the final product. The different compositions are generally translated into variations in thickness, absorbency, and softness. Several methods exist to produce nonwoven fabrics, and in this study we used fabrics manufactured by spunlace technology. The resulting dimensional properties of the nonwo- ven fabric, including surface density, thickness, porosity (ratio of void volume to total fabric volume), pore size, and structure, would mainly affect the fiber strength, flexibility, ab- sorbency, and liquid diffusion behavior. In general, higher volume porosity gives a higher vertical wicking rate, regardless of the content of the hydrophilic/hydrophobic fibers Cosmetics 2021, 8, 73. https://doi.org/10.3390/cosmetics8030073 https://www.mdpi.com/journal/cosmetics