SDR16C5 is a short-chain dehydrogenase/reductase enzyme that functions as an NAD+-dependent oxidoreductase capable of bidirectional catalytic activity 1. Its primary enzymatic function involves oxidizing all-trans-retinol to all-trans-retinaldehyde, with no activity detected toward 11-cis-retinol substrates 1. Beyond retinoid metabolism, SDR16C5 plays a central role in fatty alcohol and aldehyde metabolism in vivo, selectively oxidizing a wide range of straight-chain fatty alcohols to fatty aldehydes in meibomian glands, thereby maintaining the balance between fatty acids, fatty alcohols, and aldehydes 2. This metabolic function is particularly relevant in tissues like hair follicles, where SDR16C5 localizes to refractory telogen follicles and may contribute to vitamin A-dependent inhibition of hair follicle stem cells 3. Clinically, SDR16C5 has emerged as a diagnostic and prognostic biomarker across multiple malignancies. Its upregulation is associated with pancreatic cancer diagnosis with high sensitivity and specificity 4, correlates with HPV-positive oropharyngeal squamous cell carcinoma status 5, and serves as a prognostic gene signature component in colorectal cancer prognosis prediction 6. Additionally, SDR16C5 is elevated in various idiopathic interstitial pneumonias subtypes 7, suggesting broader disease relevance in inflammatory and fibrotic conditions.