Sphingosine is an amino alcohol most commonly characterized by an 18-carbon unsaturated hydrocarbon chain sphingosine (d18:1) . However, the hydrocarbon chain length of sphingosine, and the related dihydrosphingosine, can vary from 12-26 carbons in mammalian tissues. Sphingosine (d17:1) is a naturally-occurring but uncommon form of sphingosine, accounting for approximately 13% of the sphingosine in human skin. It can be phosphorylated by sphingosine kinases to produce C-17 sphingosine-1-phosphate. More commonly, sphingosine C-17 is used as an internal standard in the analysis of sphingoid compounds by chromatographic or spectrometric methods.