Gut Microbiome Dysbiosis in Atopic Dermatitis: Pathogenic Mechanisms, Gut–Skin Axis Disruption, and Emerging Microbiota-Targeted Therapies

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by epidermal barrier dysfunction, immune dysregulation, and marked clinical heterogeneity. Growing evidence implicates the gut microbiome in AD-related pathways through microbial metabolites, intestinal barrier function, and systemic immune signaling. This narrative review synthesizes current evidence on gut microbial alterations in AD, with particular attention to short-chain fatty acids, tryptophan-derived aryl hydrocarbon receptor ligands, intestinal permeability, gut–skin microbiome interactions, and microbiota-targeted interventions. Human studies have reported associations between AD and altered abundance of selected microbial taxa, metabolite profiles, and markers of intestinal barrier dysfunction, whereas animal and in vitro studies provide complementary mechanistic evidence. However, findings remain heterogeneous across age groups, disease phenotypes, geographic populations, analytical platforms, and treatment exposures, and causality is incompletely established. Probiotic and synbiotic interventions have shown strain-specific and context-dependent effects, while postbiotics, fecal microbiota transplantation, washed microbiota transplantation, and metabolite-directed approaches remain investigational. AI-assisted multi-omics methods may improve biological stratification and hypothesis generation, but current applications are limited by small sample sizes, cohort heterogeneity, overfitting, insufficient external validation, and limited clinical implementation. Current evidence therefore supports the gut microbiome as a mechanistically plausible contributor, potential biomarker, and therapeutic target in AD while underscoring the need for longitudinal, phenotype-aware, and externally validated studies before routine clinical translation.