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.