Catalyzes the hydroxylation of free fatty acids at the C-2 position to produce 2-hydroxy fatty acids, which are building blocks of sphingolipids and glycosphingolipids common in neural tissue and epidermis (Probable). FA2H is stereospecific for the production of (R)-2-hydroxy fatty acids (By similarity). Plays an essential role in the synthesis of galactosphingolipids of the myelin sheath (PubMed:17901466). Responsible for the synthesis of sphingolipids and glycosphingolipids involved in the formation of epidermal lamellar bodies critical for skin permeability barrier (By similarity). Participates in the synthesis of glycosphingolipids and a fraction of type II wax diesters in sebaceous gland, specifically regulating hair follicle homeostasis. Involved in the synthesis of sphingolipids of plasma membrane rafts, controlling lipid raft mobility and trafficking of raft-associated proteins (By similarity). a 1,2-saturated fatty acid + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = a (R)-2-hydroxy fatty acid + 2 Fe(III)-[cytochrome b5] + H2O 2 Fe(II)-[cytochrome b5] + 2 H(+) + hexadecanoate + O2 = (R)-2-hydroxyhexadecanoate + 2 Fe(III)-[cytochrome b5] + H2O 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 + octadecanoate = (R)-2-hydroxyoctadecanoate + 2 Fe(III)-[cytochrome b5] + H2O docosanoate + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = 2-hydroxydocosanoate + 2 Fe(III)-[cytochrome b5] + H2O 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 + tetracosanoate = (R)-2-hydroxytetracosanoate + 2 Fe(III)-[cytochrome b5] + H2O Binds 2 Zn(2+) ions per subunit that likely form a catalytic dimetal center. Lipid metabolism; fatty acid metabolism. Sphingolipid metabolism; galactosylceramide biosynthesis. Detected in oligodendrocytes (at protein level). Detected in sciatic nerve. Detected at low levels in sciatic nerve from newborns. Levels increase strongly during the first 3 weeks, and decrease thereafter to reach a low, constitutive level in 4 week olds. Expressed at a low, constitutive level in adults. Up-regulated in sciatic nerve during myelination. Up-regulated in differentiating cultured Schwann cells. The histidine box domains may contain the active site and/or be involved in metal ion binding. The N-terminal cytochrome b5 heme-binding domain is essential for catalytic activity. Belongs to the sterol desaturase family. SCS7 subfamily.