Gut Dysbiosis and the Molecular Landscape of the Gut–Skin Axis: Comparative Insights and Therapeutic Implications for Atopic Dermatitis and Psoriasis

Chronic inflammatory skin diseases, including atopic dermatitis (AD) and psoriasis, are systemic immune-mediated disorders driven by dysregulated immune responses. The gut–skin axis is a bidirectional network linking intestinal microorganisms, their metabolites, and host immunity. It connects microbiome composition and function with systemic inflammation and cutaneous pathology, shaping disease-specific mechanisms such as Th2/IL-4/IL-13-mediated barrier dysfunction in AD and Th17/IL-23/IL-17-driven hyperproliferation in psoriasis. Microbiota-derived metabolites, including short-chain fatty acids, tryptophan-derived aryl hydrocarbon receptor ligands, and bile acid-dependent FXR/TGR5 signaling, modulate immune homeostasis and epithelial integrity. Gut dysbiosis, impaired metabolite production, and barrier dysfunction disrupt regulatory networks, amplifying inflammation. Microbiota-targeted interventions, including probiotics, synbiotics, postbiotics, and precision nutrition, may serve as adjunctive therapies, although further well-controlled clinical studies are needed. Integrating multi-omics, metabolomics, and functional microbial profiling, alongside investigations of the gut mycobiome and virome, will be critical to identify predictive biomarkers and optimize therapeutic strategies. These concepts remain mechanistically compelling but largely theoretical, requiring validation in longitudinal and interventional studies.