Abstract
Recent cosmetic and dermatological science focuses on active ingredients in order to support the biological function of the skin such as protection against physical and chemical stress, UV-irradiation and microbes. Keratinocytes represent key elements of this barrier since they form the outer water-impermeable layers of the skin. To assure this function keratinocytes run through a special differentiation process from stratum basale to the stratum corneum, which is formed only of end-differentiated keratinocytes, now called corneocytes.