The Roles of Postbiotics in Modulating the Gut-skin Axis in Atopic Dermatitis: A Scoping Review

Abstract

Atopic dermatitis (AD) is a persistent inflammatory condition, where immune dysregulation, skin barrier disruption, and alterations in gut microbiota converge along the gut-skin axis. This scoping review maps the existing evidence on postbiotics’ role in modulating the gut-skin axis in AD. A total of 23 peer-reviewed articles were included in the review, comprising 5 human clinical studies, 3 animal studies, 3 in vitro studies, and 12 systematic reviews or position papers. The most frequently investigated postbiotic components were short-chain fatty acids (n = 5), heat-killed or inactivated bacterial preparations (n = 6), and microbial cell components or metabolites (n = 4). Most studies focused on immune modulation (n = 14), followed by barrier function (n = 10), and microbiota-related outcomes (n = 6). Of the human clinical studies, 60% (n = 3) evaluated oral postbiotic interventions, while 40% (n = 2) assessed topical formulations. The majority of animal and in vitro studies reported improvements in skin barrier integrity, including enhanced keratinocyte differentiation and reduced transepidermal water loss (TEWL) (n = 6 studies). A subset of studies (n = 6) demonstrated reductions in pro-inflammatory cytokines such as TNF-α and IL-6, and modulation of T-cell balance. Microbiota-related outcomes were less frequently reported, with three studies suggesting postbiotics’ potential influence on microbial composition and short-chain fatty acid production. Despite these promising findings, substantial heterogeneity was observed across studies with respect to postbiotic type, study design, and outcome measures, leading to limited standardization. This review underscores the need for further high-quality, well-powered human clinical trials using standardized postbiotic interventions to explore their therapeutic potential in AD. Future research should also address gaps in the understanding of the effects of specific postbiotics on both immune and barrier functions.