Lipid — refers to fat or fat-like substances (oils, waxes), and encompasses diverse compounds, including triglycerides, phospholipids, and sterols such as cholesterol. Lipids are an important element for the corneum layer’s healthy structure and function. They account for a significant volume of the stratum corneum, constituting 6 - 10 % of the normal corneum layer by weight. Lipids incorporated into cosmetics help moisturize the skin by renewing its barrier function, either by replacing lipids that have been removed with washing, by allowing epidermal lipids to remain despite adverse environments, or by renewing the skin’s ability to bind moisture. The skin’s barrier function against moisture loss is proportional to the corneum layer’s lipid content.