Restoring Skin Hydration and Barrier Function: Mechanistic Insights Into Basic Emollients for Xerosis Cutis

Abstract

Healthy skin is structured to maintain water balance by maximizing water retention and minimizing evaporative loss. The water-holding and barrier functions of the skin can be impaired by several factors that lead to xerosis cutis (dry skin); however, they can also be restored by basic emollients that act through the physicochemical properties of their constituents. This article aims to give a narrative review of the physiology of normal skin hydration, the key pathophysiological mechanisms implicated in dry skin, and the functional effects of basic emollients for managing xerosis cutis. Skin hydration is primarily mediated by the stratum corneum (SC), the outermost layer of the epidermis. Hygroscopic compounds in the SC maintain the skin's water-binding capacity, while the intercellular lipid bilayer and outer hydrolipid film prevent evaporative water loss. Xerosis cutis is characterized by a reduction in natural moisturizing factors or hydrolipids in the SC; it may be caused by exogenous triggers (e.g., cold weather, lifestyle, pollution), endogenous factors (e.g., aging, medication use) or genetic predisposition (as seen in atopic dermatitis, psoriasis, ichthyosis), or it may present as a symptom of a systemic disease (e.g., diabetes mellitus, hypothyroidism). Regardless of the underlying cause, basic emollients are recommended for the treatment of xerosis cutis and are typically formulated with humectants to improve skin hydration and water-holding capacity (e.g., glycerol, urea, lactic acid) and occludents to restore the epidermal barrier (e.g., petrolatum, liquid paraffin). Basic emollients remain the standard of care for the long-term management of xerosis cutis and diseases associated with dry skin.