Skin Lipid Dysregulation in Atopic Dermatitis and Related Inflammatory Skin Diseases.

Epidermal lipids are essential for skin barrier function and actively influence cutaneous immune homeostasis. Recent advances have transformed our understanding of skin lipid dysregulation in allergic diseases, revealing complex bidirectional relationships between barrier dysfunction and immune activation. This review provides a comprehensive analysis of the 2020-2025 literature on skin lipid metabolism in allergic and inflammatory diseases, with a particular focus on molecular mechanisms, diagnostic biomarkers, therapeutic advances, and implications for precision medicine. Key discoveries include the finding that sphingomyelin deacylase, long linked to ceramide (CER) deficiency, is actually the β-subunit of acid ceramidase. In atopic dermatitis, this enzyme shifts its substrate specificity to sphingomyelin, depleting the barrier lipid pool. Type 2 cytokines, particularly interleukin (IL)-4 and IL-13, suppress lipid biosynthesis through Janus kinase (JAK)/Signal Transducer and Activator of Transcription 6-mediated downregulation of fatty acid (FA) elongases. This suppression, particularly affecting elongation of very long-chain fatty acid (ELOVL) enzymes, such as ELOVL1, ELOVL3, and ELOVL6, disrupts the synthesis of ultra-long-chain CERs essential for barrier function. JAK inhibitors effectively reverse T helper 2 (Th2)-mediated lipid suppression, while optimized topical lipid ratios (3:1:1 CER: cholesterol: FA) enhance barrier repair. Innovations, such as lipid nanoparticles and microbiome-modulating therapies, further support personalized treatment strategies. The integration of barrier repair with targeted immunomodulation-guided by lipidomic and genomic profiling-marks a paradigm shift toward predictive and preventive approaches in allergic skin diseases. Early intervention strategies that simultaneously address immune dysregulation and lipid metabolism hold promise for preventing the atopic march and sustaining long-term remission.