The Skin Barrier and Moisturization: Function, Disruption, and Mechanisms of Repair.

BACKGROUND: The anatomic layers of the skin are well-described; recent research into the barrier capabilities of the skin has led to the development of a functional model of the skin barrier. Moisturization has been consistently recommended for use in conditions such as atopic dermatitis, in which barrier disruption plays a key role in disease. This review aims to analyze the skin barrier in the context of this function model, with a focus on the mechanisms by which moisturizers support each of the functional layers of the skin barrier to promote homeostasis and repair.

METHODS: A PubMed literature search was conducted using combinations of the search terms "skin barrier", "functional skin barrier", "acid mantle", "skin microbiome", "moisturizer", "emollient", "humectant", and "occlusive" to uncover relevant articles. Abstract review was conducted to determine relevance for inclusion; references of articles were also reviewed and included as needed. The article search was limited to articles published in English.

RESULTS: The skin barrier is comprised of four interdependent layers - physical, chemical, microbiologic, and immunologic - which maintain barrier structure and function. Skin barrier disruption affects each of these four layers; moisturizers target each of these layers to promote homeostasis and repair. Occlusives, humectants, and emollients occlude the surface of the stratum corneum, draw water from the dermis into the epidermis, and assimilate into the stratum corneum, respectively, in order to strengthen the physical skin barrier. Acidic moisturizers bolster the chemical skin barrier by supporting optimal enzymatic function, increasing ceramide production, and facilitating ideal conditions for commensal microorganisms. Regular moisturization may strengthen the immunologic skin barrier by reducing permeability, allergen penetration, and sensitization.

CONCLUSIONS: The physical, chemical, microbiologic, and immunologic layers of the skin barrier are each uniquely impacted in states of skin barrier disruption. Moisturizers target each of the layers of the skin barrier to maintain homeostasis and facilitate repair.