Our skin produces a protective layer of oil, called sebum, that includes a balance of ceramides, cholesterol and fatty acids. This layer is called the acid mantel and is a very important feature of healthy, balanced skin. Serving a very important protective function, the slightly acidic pH of the acid mantle creates an environment that is not conducive to bacteria or yeast overgrowth. It also creates a waterproof layer that protects against moisture loss from the epidermis. Over-cleansing, dry air and environmental pollutants have the potential to disrupt the balance of the acid mantel, rendering the skin vulnerable to damage, dryness, infection and disease. The fatty acids in skin care oils offer a way to replenish and renew the acid balance, especially immediately after cleansing. Soap and surfactant based cleansers do dissolve excess oil and carry away dirt and dead skin cells, but they also essentially strip away the protective acid mantel while turning the slightly acid pH to a more caustic base pH. It is vitally important to replenish the acid mantel with fatty acids present in skin care oils after cleansing.