Modulating the Gut–Skin Axis in Dermatological Diseases: Mechanisms and Clinical Applications of Probiotics, Prebiotics, Synbiotics, and Postbiotics

The gut–skin axis represents a bidirectional regulatory network linking intestinal microbiota composition and function to cutaneous inflammation and barrier integrity through interconnected immune, metabolic, barrier-related, and neuroendocrine pathways. Key mechanisms include microbiota-driven immune modulation, production of short-chain fatty acids (SCFAs), regulation of epithelial permeability and lipopolysaccharide (LPS) translocation, and modulation of the hypothalamic–pituitary–adrenal (HPA) axis and insulin-like growth factor-1 (IGF-1) signaling. Increasing evidence supports the role of these pathways in the pathogenesis and clinical course of inflammatory dermatological diseases, including atopic dermatitis, acne vulgaris, rosacea, and psoriasis. This narrative review critically evaluates current experimental and clinical evidence on probiotics, prebiotics, synbiotics, and postbiotics as therapeutic modulators of the gut–skin axis in dermatology. A targeted literature search covering the period 2000–2025 was conducted using PubMed/PMC, Scopus, Web of Science, and Google Scholar, prioritizing systematic reviews, meta-analyses, and randomized controlled trials reporting clinically relevant outcomes. Available data indicate that selected Lactobacillus and Bifidobacterium strains are associated with improvements in skin barrier function, modulation of inflammatory responses, and clinically meaningful benefits, most consistently in atopic dermatitis. The strongest evidence supports preventive and adjunctive use in pediatric atopic dermatitis. In acne vulgaris, psoriasis, and rosacea, reported efficacy appears moderate and heterogeneous, reflecting substantial variability in strains, formulations, dosing regimens, and study design. Prebiotics and synbiotics demonstrate favorable effects on microbial balance and inflammatory activity, while postbiotics and microbiota-modulating topical agents represent emerging therapeutic approaches with promising safety and tolerability profiles. Overall, microbiota-targeted interventions act on distinct nodes within the gut–skin axis and may serve as rational adjunctive strategies in selected dermatological conditions. However, clinical efficacy is strain- and formulation-specific, and further well-designed, adequately powered, and mechanism-driven clinical trials are required to define their precise role in routine dermatological practice.