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Recent Advances in Mild and Moisturizing Cleansers

January 2019 | Volume 18 | Issue 1 | Supplement Individual Articles | 80 | Copyright © January 2019


KP Ananthapadmanabhan PhD,a James J. Leyden MD,b Stacy S. Hawkins PhDc

aJL Winkle College of Pharmacy, University of Cincinnati, Cincinnati, OH bDepartment of Dermatology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA cUnilever Research & Development, Trumbull, CT

Figure1Figure2The results in Figure 1 show that anionic surfactants are harsher than amphoteric and nonionic surfactants and addition of amphoteric surfactants to anionics make them milder. This assay has been previously validated for its correlation with in vivo evaluation of formulation mildness and irritancy potential.14 It is evident from the past work that the charge of the surfactant plays a role in their irritation potential. Further research along these lines has led to the development of a quantitative relationship between the charge density of surfactant micelles (self-assembled surfactant aggregates in solution) in the cleanser system and their skin irritation potential (see Figure 2).22 Such quantitative structure–function relationships will help formulators assess the relative irritation potential of technologies prior to expensive clinical studies.The reason SC swelling by surfactants correlates with skin irritation is because, upon swelling, the permeability of the structure increases, significantly leading to penetration of foreign materials into deeper layers causing a biochemical reaction that manifests as irritation, inflammation, and itch.The inherent irritation potential of surfactants and other chemicals to skin can be determined from keratinocyte cell culture studies or living skin equivalent (LSE) models studies in which irritation can be related to the release of inflammatory biomarkers such as IL1 alpha (interleukin 1α (IL1-α) and IL1-Ra).23,24 Since these systems do not have a fully developed corneum barrier, they may not predict the irritation potential under normal use conditions. However, such testing may be appropriate for testing products intended for compromised skin situations such as those in sensitive, atopic, and infant skin.Surfactant Interactions With Skin Lipids Surfactants are designed to interact with fatty materials such as sebum and skin lipids. While removal of sebum is important during cleansing, interaction with SC bilayer lipids is not desirable as the latter constitutes the main barrier to water transport through skin. Cleanser surfactants can intercalate into the bilayer and increase its permeability by altering the bilayer structure.4,25 It can also extract the “more extractable” lipids such as medium chain fatty acids (eg, palmitic or stearic acid) and cholesterol and affect the skin permeability.4, 25-28 A quantitative determination of the amount of SC bilayer lipids during cleansing has been a challenge because of their complexity in terms of chain length and the absolute amounts involved.28 Superficial effects of surfactants on skin lipids may not immediately lead to skin irritation, but may manifest as skin dryness.4, 27 With continued damage, such a situation can progressively result in scaling, flaking, and disruption of barrier.Several in vitro methods exist to estimate the tendency of surfactants to damage SC lipids.4, 25-29 This includes simple assays