Effects of Probiotic Supplementation in Adults with Atopic Dermatitis: A Meta-Analysis

Background: Atopic Dermatitis (AD) in adults is a troublesome condition to treat because of its chronic condition and side effects of prolonged traditional treatments. Probiotics, with their use of the gut-skin axis, are an emerging adjunct treatment by controlling immune effects and facilitating dermal health. This systematic review discusses the efficacy, safety and mechanism of action of probiotic supplementation for adult AD. Methods: We had 13 studies, 7 on Lactobacillus spp. (224 patients) and 6 on mixtures of probiotics (878 patients), in total 1,102 patients, with follow-up between 8 weeks and 12 months. Outcomes were AD severity (SCORAD/EASI), immunological and microbiome alterations, Quality of Life (QoL) and safety. Random-effects meta-analysis was performed where data allowed and qualitative themes were coded to elucidate mechanisms and implications. Results: Probiotics, compared to placebo, significantly lowered AD severity (pooled Mean Difference MD = -12.3, 95% CI: -15.6 to -9.0, P<0.001), more in mild AD (MD = – 14.2) than in moderate-to-severe AD (MD = -10.8). Lactobacillus strains (e.g., L. salivarius LS01; 52.3% decrease) and multi-strain combinations (e.g., L. rhamnosus GG, L. casei, B. longum; 39.5% decrease) were equally effective, an effect borne out by recent meta-analyses (SMD: -4.0, 95% CI: -7.3 to -0.7). Immunologically, probiotics enhanced Th1/Th2 equilibrium (↓IL-4, ↑IFN-γ), suppressed IgE and elevated regulatory T-cells. Microbiome modulation entailed enhanced gut species richness and attenuated S. aureus colonization, strengthening the gut-skin axis. QoL was enhanced (e.g., DLQI change) and corticosteroid requirements declined. Safety was optimal, with few side effects (e.g., occasional gastrointestinal upset). Conclusion: Probiotic supplementation is a safe, efficacious adjunctive treatment for adult AD, but mild-to-moderate AD only, with decreased severity, immune modulation, quality of life improvement and decreased reliance on traditional treatments. While there are consistent findings, heterogeneity (I²=65%, P<0.01) and short follow-ups call for large, standardized RCTs to establish long-term efficacy and streamline strain-specific protocols. Through June 05, 2025, probiotics hold strong potential to fill gaps in AD treatment, with potential implications for personalized therapeutic approaches.