C18 Phytoceramide (t18:0/18:0) (Cer(t18:0/18:0)) is a bioactive sphingolipid found in the stratum corneum of Saccharomyces cerevisiae, wheat grain, and mammalian epidermis. Cer(t18:0/18:0) consists of a phytosphingosine backbone amine linked to a C18 fatty acid chain. Cer(t18:0/18:0) has the function of regulating apoptosis, cell differentiation, proliferation of smooth muscle cells and inhibition of mitochondrial respiratory chain. It also suppresses the expression of allergic cytokines IL-4, TNF-α, and transcription factors c-Jun and NF-κB in histone-stimulated mouse skin tissue. Formulations containing cer(t18:0/18:0) have been used as skin protectants in cosmetics as they reduce water loss and prevent epidermal dehydration and irritation.