08/22/2026
Skin Barrier Facts: The term “skin barrier” usually refers to the stratum corneum (SC), which is crucial for maintaining skin integrity. The SC includes corneocytes, intercellular lipid lamellae, corneodesmosomes, and tight junctions. Its stability relies on three main elements: lipids within the SC, natural moisturizing factors (NMFs), and the skin’s acidic pH. Skin acidity is maintained through three internal processes: free fatty acids from phospholipids, trans-urocanic acid from filaggrin (FLG), and the sodium-hydrogen exchanger (NHE). The NHE is a membrane protein that uses the sodium gradient to transport ions, playing a key role in functions like regulating intracellular pH. The stratum corneum acts as the primary permeability barrier, often described as ‘bricks and mortar,’ with corneocytes as bricks and extracellular lipids as mortar. Important barrier lipids—ceramides, cholesterol, and free fatty acids—are organized in lamellae to prevent water loss and block external agents. Keeping the skin’s pH slightly acidic is vital for barrier stability and proper lipid processing. Extracellular calcium is essential for establishing and signaling the skin's calcium gradient, which activates repair responses when the barrier is damaged. Its distribution enables dynamic changes that support keratinocyte functions such as differentiation, barrier formation, and skin homeostasis. Disruption of this calcium gradient—commonly caused by barrier injury—triggers the secretion of lipid barrier components and initiates repair processes. Acute damage causes a rapid drop in extracellular calcium, especially in the upper stratum granulosum, disturbing the calcium gradient. Usually, within 6 to 24 hours, calcium levels in the upper epidermis gradually recover as the barrier heals.
