ARTICLE: Compromised Skin Barrier and Sensitive Skin in Diverse Populations

April 2021 | Volume 20 | Issue 4 | Supplement Individual Articles | s17 | Copyright © April 2021


Published online April 6, 2021

Yan Wu MD PhDa, Janet Wangari-Olivero PhDb, Yaxian Zhen MD PhDb

aDepartment of Dermatology, Peking University, First Hospital, Beijing, China
bL’Oréal Research and Innovation, Clark, NJ

Abstract
The most important function of the stratum corneum (SC), the uppermost layer of the human epidermis, is the formation of the epidermal permeability barrier. Lipids, particularly ceramides, cholesterol, and free fatty acids, together form lamellar membranes in the extracellular spaces of the SC that limit the loss of water and electrolytes. In addition to preventing water and electrolyte loss, the SC as a permeability barrier prevents the entry of harmful irritants, allergens, and microorganisms into the skin. Disruption of the epidermal barrier leads to skin that is irritated, more reactive, and more sensitive than normal skin. SC thickness, lipid profile, and barrier function vary with different ethnic groups, which is also reflected the differences in prevalence and manifestation of diverse skin conditions related to the skin barrier function such as atopic dermatitis and sensitive skin. In addition to these compromised skin barrier related conditions, we are just now starting to understand the direct and indirect impact of COVID-19 on the skin and how current preventative measures are contributing to skin barrier disorders. Our understanding of various approaches for restoration of skin barrier, especially the role of topically applied mixtures of cholesterol, ceramides, and essential/nonessential free fatty acids (FFAs) allows for the strengthening of the compromised skin barrier and alleviation of symptoms and discomfort associated with skin barrier disorders. Ceramide containing products on the market are commonly available and offer protection and reparative benefits to the skin barrier.

J Drugs Dermatol. 20(4 Suppl):17-22. doi:10.36849/JDD.S589C

INTRODUCTION

“A pivotal point of terrestrial adaptation is prevention of desiccation and maintenance of internal water homeostasis”.1 The critical role of the stratum corneum (SC) permeability barrier is the protection of the human body from desiccation by limiting transcutaneous movement of water and electrolytes, as well as preventing the entry into the skin of harmful substances like irritants, allergens, and microorganisms. The SC lipids, particularly ceramides, cholesterol, and free fatty acids together forming lamellar membranes in the extracellular spaces of the SC, play a key role in the integrity of SC permeability barrier commonly referred to as epidermal barrier, or skin barrier.1 The intercellular lipids of the SC together with intracellular humectants (natural moisturizing factor, NMF) endow the SC with softness and flexibility by their water holding capacity.2,3 Disruption of the epidermal barrier leads to alterations of SC proteins and lipids, increased transepidermal water loss (TEWL), decreased skin hydration status (clinically seen as dry skin), decreased skin elasticity and smoothness, increased skin reactivity to external stimuli,2,3 and even skin diseases. This review summarizes current understanding of skin barrier integrity and function, clinical consequence of impaired skin barrier integrity, impact of COVID-19 on skin health, sensitive skin in diverse populations, and management strategies.

Ethnicity and Skin Barrier Function
Several methods have been used to understand differences in skin barrier among Caucasian, Asian, and African American ethnic groups including the measurement of TEWL, tape stripping to examine stratum corneum layers, lipid content analysis, and irritation with sodium lauryl sulfate.4,5,6 For TEWL, the evidence indicates that African American skin has greater TEWL than Caucasian skin.5 However, for Asians, the data is inconsistent, with some studies showing TEWL similar to African American skin7 and some showing TEWL lower than Caucasian or Hispanic skin. Other studies have compared differences of skin barrier in different skin pigmentation types (Fitzpatrick phototypes) instead of ethnicity. The study by Reed et al comparing Fitzpatrick skin type II and III of Asians and Caucasians to types IV and VI of Asian, Hispanic, and African American backgrounds with TEWL measured after tape stripping, showed that phototypes IV and V required more tape stripping than phototypes II and III to achieve the same TEWL.8 This led to the conclusion that darker skin may have better barrier integrity and is thus able to withstand insults more than lighter skin. Other studies have supported this theory by demonstrating that African American skin has more corneocyte layers, with a more compactly packed stratum corneum due to increased intercellular cohesiveness.9,10 This connection of