Phytosphingosine is a phospholipid. It’s a long-chain, complex fatty alcohol that’s naturally found in the outermost layer of the skin. It functions as a moisturising water-binding agent and has some preservative qualities.
Phytoshingosine is found abundantly in fungi, plants, and animals. It’s shown to achieve its moisturizing effect by modulating pathways that are directly responsible for natural moisturizing factor (NMF) production.1 The NMF is a collection of substances that work to keep the skin barrier intact and flourishing.
 Choi, Hyun & Cho, Young & Lee, Eun & Kim, Jin Wook & Park, Chang. (2017). Phytosphingosine enhances moisture level in human skin barrier through stimulation of the filaggrin biosynthesis and degradation leading to NMF formation. Archives of Dermatological Research. 309. 10.1007/s00403-017-1782-8.