Healthy skin starts with a healthy skin barrier!
A skin barrier acts like a guard that distinguish between the substances that are allowed to enter the skin from those that must be kept outside. The outermost layer of the skin-epidermis has a thin layer of non-living skin cells known as Stratum Corneum. This Stratum Corneum represents the skin barrier. It is 'Stratum Corneum' with which all the products interact.
A skin barrier prompts an anti-inflammatory in response to products. It helps in maintaining the moisture balance of the skin and the integrity of skin function. Structurally, it follows brick and mortar analogy, where bricks represent the non-living cells while the mortar represents intercellular lipids (includes ceramides, cholesterol, and fatty acids). Any disturbance in this arrangement, either disruption of cells or of lipids, leads to a barrier defect (just like a wall cannot stand if either of the brick or the mortar is missing). Skin barrier may get damaged for various reasons such as the use of harsh products, excessive exfoliation, neglected skin, exposure to an extreme environment (too hot or too cold water), excessive washing, etc.