Human epidermis displays a characteristic calcium gradient, with low calcium levels in the basal and spinous layers, but increased progressively towards the outer stratum granulosum. The distribution pattern of ionic calcium correlates with growth and differentiation of keratinocytes, as low extracellular calcium concentrations stimulate the growth of keratinocytes with high proliferation rate, and a high extracellular calcium levels induce differentiation and stratification. However, such a gradient is not observed in skin abnormalities related to the formation of abnormal barrier function, such as psoriasis. Also, acute disruption of the epidermal permeability barrier causes an influx of water into stratum corneum and immediate loss of calcium gradient. Subsequently, this depletion of calcium gradient regulates lamellar body exocytosis, and the restoration appears in parallel with barrier recovery. The regulation of calcium in skin is therefore requisite to maintain a normal skin barrier function and to avoid dry skin symptoms. Furthermore, extracellular calcium ions are important for cell-cell adhesion and epidermal differentiation.