CYP2S1 is a cytochrome P450 monooxygenase predominantly expressed in epithelial tissues of portal-of-entry organs including the respiratory tract, gastrointestinal tract, and skin 1. The enzyme catalyzes oxidative metabolism of retinoids, particularly all-trans-retinoic acid in the epidermis, utilizing molecular oxygen and electrons from NADPH via cytochrome P450 reductase 2. Beyond monooxygenase activity, CYP2S1 displays peroxidase and isomerase activities toward eicosanoids, efficiently metabolizing prostaglandins and hydroperoxyeicosatetraenoates to products including 12-hydroxy heptadecatrienoic acid, malondialdehyde, and thromboxane A2 3. This peroxide metabolism occurs independently of NADPH and cytochrome P450 reductase, suggesting a distinct catalytic mechanism. CYP2S1 expression is induced by dioxin through the aryl hydrocarbon receptor pathway 1. The enzyme metabolizes xenobiotics including naphthalene and carcinogens, potentially contributing to tissue-specific toxicity 4. Recent evidence indicates CYP2S1 regulates the intestinal metabolome and microbiome, with altered expression associated with inflammatory bowel disease 5. Abnormal CYP2S1 gene methylation has been documented in high-altitude pulmonary edema patients 6, suggesting epigenetic involvement in disease pathogenesis.