DEGS2 (delta 4-desaturase, sphingolipid 2) is a bifunctional enzyme localized to the endoplasmic reticulum that catalyzes both sphingolipid delta-4 desaturation and C4-monooxygenation activities 1. The enzyme primarily converts dihydrosphingosine-ceramides to phytosphingosine-ceramides (PHS-CERs) via hydroxylation, with preferential activity toward substrates containing very-long-chain fatty acids (≥C21) 1. DEGS2 expression is tightly regulated by inflammatory cytokines: Th2 cytokines upregulate DEGS2 in keratinocytes, while Th1/Th17 cytokines downregulate it, contributing to distinct lipid barrier alterations in atopic dermatitis versus psoriasis 2. Mechanistically, DEGS2-synthesized phytoceramides activate PI3K-AKT signaling to promote cancer stem cell traits in prostate cancer 3, while m6A methylation-mediated DEGS2 upregulation suppresses ceramide synthesis in colorectal cancer progression 4. Genetic variants in DEGS2 (rs3783332, rs7157599) are associated with cognitive deficits in schizophrenia and regulate DEGS2 brain expression 5. In eosinophilic esophagitis, decreased DEGS2 expression correlates with altered sphingolipid composition and epithelial barrier dysfunction 6. DEGS2's role in ceramide biosynthesis is essential for maintaining epithelial integrity while also contributing to pathological conditions including cancer progression, inflammatory skin diseases, and gastrointestinal disorders.