Skin Barrier (Moisture Barrier)

The skin barrier is the outermost defensive layer of the skin, formed mainly by the stratum corneum, that keeps water in and irritants, allergens and microbes out. It is often described with a "brick and mortar" model: flattened dead skin cells (corneocytes) are the bricks, while a lipid matrix of ceramides, cholesterol and free fatty acids acts as the mortar sealing the spaces between them.

This lipid mortar is what limits transepidermal water loss and blocks the entry of external aggressors. When the ratio of these lipids is disrupted, or the barrier is physically damaged, the skin loses water more easily and becomes more reactive. Common signs of a compromised barrier include tightness, stinging on application of products, redness, flaking and increased sensitivity.

Barrier disruption can follow over-exfoliation, harsh cleansing, high concentrations of actives, cold or dry weather, and frequent physical scrubbing. Supporting the barrier generally means reducing the number of stripping steps, using gentle cleansers, and applying formulations that mimic or replenish skin lipids, such as ceramide-containing moisturizers, along with occlusives that reduce water loss while the barrier recovers.

• Bricks: corneocytes (dead, flattened skin cells)
• Mortar: ceramides, cholesterol and fatty acids
• Main job: hold water in, keep irritants out