The Gut-Brain-Skin Axis: Systemic Effects of Functional Ingredients in Healthy Skin Aging.

Interactions among the gut, brain, and skin are increasingly understood as a systemic regulatory network connecting intestinal activity, neuroimmune communication, and cutaneous homeostasis. Microbiota-derived metabolites, immune mediators, and neuroendocrine pathways can influence central nervous system activity and subsequently regulate skin homeostasis. This review summarizes current evidence on how functional ingredients modulate the gut-brain-skin axis in the context of aging and skin health. Polyphenols, probiotics, and omega-3 fatty acids appear to act through overlapping biological routes, including reshaping microbial communities, supporting epithelial barrier function, regulating immune activity, and limiting oxidative stress. These gut-derived signals may affect the brain through neural, endocrine, and immune pathways, thereby modulating neuroinflammation, hypothalamic-pituitary-adrenal (HPA) axis activity, and neurotransmitter balance. Through brain-skin communication, these changes may influence inflammation, epidermal barrier integrity, collagen remodeling, and skin aging processes. Emerging clinical evidence suggests potential improvements in skin-related outcomes and systemic inflammatory markers; however, studies remain heterogeneous, and integrated assessments of gut, brain, and skin endpoints are limited. Further studies that integrate multi-omics profiling with carefully designed clinical trials will be required to define causal pathways and support the development of evidence-based nutritional approaches targeting this axis.