Abstract
The skin serves the vital function of providing a barrier between the hostile external environment and the host. While the skin has many important barrier functions, the two that are absolutely essential for survival are the barrier to the movement of water and electrolytes (permeability barrier) and the barrier against invasive and toxic microorganisms (antimicrobial barrier). Lipids play an essential role in the formation and maintenance of both the permeability and antimicrobial barriers. A hydrophobic extracellular lipid matrix in the stratum corneum composed primarily of ceramides, cholesterol, and free fatty acids provides the barrier to the movement of water and electrolytes. A variety of lipids, such as fatty alcohols, monoglycerides, sphingolipids, phospholipids, and in particular free fatty acids, have antimicrobial activity and contribute to the antimicrobial barrier. In addition to these essential functions, we will also review the ability of skin surface cholesterol to reflect alterations in systemic lipid metabolism and the risk of atherosclerosis.
Highlights
The skin serves the vital function of providing a barrier between the hostile external environment and the host
While the skin has many important barrier functions, the two that are absolutely required for survival are the barrier to the movement of water and electrolytes and the barrier against invasive and toxic microbes (1)
The permeability barrier is localized to the outer layer of the epidermis, the stratum corneum (SC) (1, 2)
Summary
The permeability barrier is localized to the outer layer of the epidermis, the stratum corneum (SC) (1, 2). Following permeability barrier disruption, the increased water movement through the compromised SC carries calcium outward toward the skin surface resulting in a reduction in the calcium concentration surrounding the stratum granulosum cells (2). This change in calcium concentration appears to be the primary signal inducing lamellar body secretion. Other nonionic signals generated in the SC and by keratinocytes may influence the secretory response [for review, see (5)]. This robust homeostatic response assures that defects in permeability barrier function are rapidly corrected
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