ABSTRACT
Lipids perform various functions in cosmetic science including their role as biological structural components of skin and hair, sebum constituents, and functional ingredients in cosmetic preparations. From a biological standpoint, the plasma membrane of keratinocytes and other cells of the viable epidermis and dermis are comprised principally of phospholipids with small quantities of cholesterol, free fatty acids, and other lipids. The stratum corneum, on the other hand, mostly contains ceramides with lesser quantities of cholesterol and free fatty acids. A major consideration for all lipids related to skin and skin care technologies is their potential to become oxidized. As the outermost protective organ of the body, the skin continuously finds itself under assault from external insults. Lipids under attack by free radicals undergo oxidation reactions that alter their structure and debilitate them to the point where they can no longer perform their normal biological functions. In cell membranes, this results in loss of membrane fluidity and could disrupt membrane channels that permit the passage of ions and molecules into and out of the cell. Lipid peroxidation and its prevention are not only important in vivo but also play an important role in the stability of cosmetic products.
