Ceramides are among the most important dermal sphingolipids, which are the skin's own fats. They make up about half of the stratum corneum lipids. Ceramides have numerous structural and biological functions in the human epidermis, e.g., they are involved in preventing transepidermal water loss. In addition, ceramides regulate processes such as cell division and differentiation of keratinocytes (keratin-forming cells).(1) Ceramides are differentiated according to the length of their bound fatty acid or sphingoid backbone, e.g., into ceramides AP, NP, or EOP.(1)A study found that the facial skin of patients with mild to moderate acne vulgaris contained a significantly lower percentage of ceramides and sphingosines, while transepidermal water loss was significantly higher compared to healthy control subjects.(2) In vitro studies also showed that phytosphingosine inhibits the growth of bacteria, including Cutibacterium acnes, and subsequent in vivo studies confirmed the antimicrobial properties by significantly reducing the total bacterial count on unwashed hands. (1)