Physical barrier of skin and gut mucosa

The **physical barrier of the skin and gut mucosa** consists of highly organized epithelial structures—most prominently the stratum corneum in skin and the mucosal epithelial layer in the gut—which serve as key protective interfaces between the body and the external environment. In skin, the barrier is formed primarily by the outermost epidermal layer, the stratum corneum, which acts as a 'brick-and-mortar' structure where protein-rich corneocytes (bricks) are sealed by extracellular lipids (mortar) such as ceramides, cholesterol, and fatty acids. This barrier limits pathogen invasion, chemical exposure, water loss, and mechanical damage, and supports immune defense, pH maintenance, and normal skin microbiome composition[1][2][3][4][5]. Similar physical barriers exist in the gut, where mucosal epithelia and overlying mucus protect underlying tissues from microorganisms, toxins, and digestive enzymes. While often referred to in therapeutic contexts (e.g., in barrier repair creams or as a general concept in disease), the physical barrier itself is not a discrete molecular target (such as a single protein or receptor), but a highly integrated structure composed of various cell types and biochemical components. Thus, it is not considered a classical drug target like a receptor or enzyme. Common diseases of barrier dysfunction include atopic dermatitis, other inflammatory skin diseases, and gut inflammatory disorders. Direct repair of this barrier is often achieved through topical application of creams containing lipids or occlusive agents that restore the physical and biochemical integrity of the barrier. Note: "Physical barrier on skin/gut mucosa" is a functional/structural concept and not a single molecule or receptor, so it is not considered a classical therapeutic target. For molecular targets within these barriers (such as filaggrin, ceramides, or tight junction proteins), more specific names should be used[2][3][4].

Other names

Skin barrierEpithelial barrierMucosal barrierEpidermal barrierStratum corneum (for skin)

Physical protection; Enhancement or restoration of lipid matrix; Moisture retention; Reduction of transepidermal water loss (TEWL)