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 (PubMed:15658937, PubMed:16998236, PubMed:22517924). FA2H is stereospecific for the production of (R)-2-hydroxy fatty acids (PubMed:22517924). Plays an essential role in the synthesis of galactosphingolipids of the myelin sheath (PubMed:15658937, PubMed:18815260). 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 (PubMed:21628453). Involved in the synthesis of sphingolipids of plasma membrane rafts, controlling lipid raft mobility and trafficking of raft-associated proteins (PubMed:22517924). 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. Sphingolipid metabolism; galactosylceramide biosynthesis. Lipid metabolism; fatty acid metabolism. Expressed in brain (at protein level) (PubMed:16998236). Detected in cerebellum and forebrain (PubMed:18815260, PubMed:15658937). Expression in the white matter is mainly restricted in oligodendrocytes (PubMed:15658937). Expressed in stomach, kidney, skin and testis (PubMed:15658937). Expressed in sebaceous gland (PubMed:21628453). Levels increase rapidly in brains from newborns, in parallel with myelination in the central nervous system. Present at very low levels in newborns. Levels are highest at 2 to 3 weeks, and then decrease slightly to reach an constant, intermediate level after 4 months. Constitutively expressed at an intermediate level throughout adult life. 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. Knockout mice have normal oligodentrocyte differentiation and develope structural and functional normal myelin up to early adulthood. However, aged knockout mice show a massive axon and myelin sheath degeneration in the spinal cord (PubMed:18815260). Knockout mice show delayed fur development and a cyclic alopecia (PubMed:21628453). Belongs to the sterol desaturase family. SCS7 subfamily.