A bioactive sphingolipid found in S. cerevisiae, wheat grains, and mammalian epidermis; has a role in regulation of apoptosis, cell differentiation, proliferation of smooth muscle cells, and inhibition of the mitochondrial respiratory chain; is used in cosmetics as a skin protectant ; inhibits expression of allergic cytokines IL-4, TNF-α, and transcription factors c-jun and NF-κB in histone stimulated tissue