Catalyzes the hydrolysis of sphingomyelin to form ceramide and phosphocholine. Ceramide mediates numerous cellular functions, such as apoptosis and growth arrest, and is capable of regulating these 2 cellular events independently. Also hydrolyzes sphingosylphosphocholine. Regulates the cell cycle by acting as a growth suppressor in confluent cells. Probably acts as a regulator of postnatal development and participates in bone and dentin mineralization (PubMed:10823942, PubMed:14741383, PubMed:15051724). Binds to anionic phospholipids (APLs) such as phosphatidylserine (PS) and phosphatidic acid (PA) that modulate enzymatic activity and subcellular location. May be involved in IL-1-beta-induced JNK activation in hepatocytes (By similarity). May act as a mediator in transcriptional regulation of NOS2/iNOS via the NF-kappa-B activation under inflammatory conditions (By similarity). a sphingomyelin + H2O = an N-acylsphing-4-enine + H(+) + phosphocholine H2O + N-(15Z-tetracosenoyl)sphing-4-enine-1-phosphocholine = H(+) + N-(15Z-tetracosenoyl)-sphing-4-enine + phosphocholine H2O + N-(tetracosanoyl)-sphing-4-enine-1-phosphocholine = H(+) + N-tetracosanoyl-sphing-4-enine + phosphocholine an N-(acyl)-sphingosylphosphocholine + H2O = an N-acyl-sphingoid base + H(+) + phosphocholine 1-hexadecanoyl-sn-glycero-3-phosphocholine + H2O = 1-hexadecanoyl-sn-glycerol + H(+) + phosphocholine 1-O-octadecyl-sn-glycero-3-phosphocholine + H2O = 1-O-octadecyl-sn-glycerol + H(+) + phosphocholine a sphingosylphosphocholine + H2O = a sphingoid base + H(+) + phosphocholine H2O + N-(hexadecanoyl)-sphing-4-enine-1-phosphocholine = H(+) + N-hexadecanoylsphing-4-enine + phosphocholine Inhibited by nSMase inhibitor GW4869 (PubMed:10823942). Binding of anionic phospholipids (APLs) such as phosphatidylserine (PS) and phosphatidic acid (PA) increases enzymatic activity (By similarity). Optimum pH is 7.5. Lipid metabolism; sphingolipid metabolism. May localize to detergent-resistant subdomains of Golgi membranes of hypothalamic neurosecretory neurons (PubMed:10823942). Localizes to plasma membrane in confluent contact-inhaibited cells (PubMed:15051724). Predominantly expressed in brain. Up-regulated during G0/G1 phases. Palmitoylated, palmitoylation-deficient proteins are targeted for lysosomal degradation. Belongs to the neutral sphingomyelinase family.