Oral Probiotics for Improving Skin Hydration, Elasticity, Transepidermal Water Loss, and Wrinkle Reduction in Adults: A Systematic Review and Meta‐Analysis of Randomized Controlled Trials

ABSTRACT Background The gut‐skin axis has emerged as a potential target for skin health interventions. Oral probiotic supplementation may improve skin outcomes through immunomodulatory and anti‐inflammatory mechanisms, yet evidence remains inconsistent. Objective To systematically review and meta‐analyze randomized controlled trials (RCTs) assessing the effects of oral probiotic supplementation on skin hydration, transepidermal water loss (TEWL), elasticity, and wrinkle appearance in healthy adults. Methods We searched Cochrane CENTRAL, Embase, PubMed, Scopus, Web of Science, and Google Scholar from inception to August 2025 without language restrictions. Two independent reviewers screened 390 records, assessed 28 full‐text articles, and extracted data from 15 eligible RCTs (867 participants). Risk of bias was assessed using the Cochrane RoB 2 tool. Random‐effects meta‐analyses (DerSimonian–Laird method) calculated pooled standardized mean differences (SMD, Hedges' g) with 95% confidence intervals. Heterogeneity was quantified using I 2 statistics. GRADE methodology assessed certainty of evidence. This systematic review protocol was registered with PROSPERO (CRD420251123389). Results Compared to placebo, oral probiotics significantly improved skin hydration (5 RCTs, n = 402; SMD = 1.208, 95% CI [0.410, 2.006], p = 0.003, I 2 = 87.5%), reduced TEWL (6 RCTs, n = 453; SMD = −1.165, 95% CI [−1.402, −0.927], p < 0.0001, I 2 = 4.7%), and decreased wrinkle scores (4 RCTs, n = 287; SMD = −1.299, 95% CI [−1.736, −0.863], p < 0.0001, I 2 = 80.0%). Effects on skin elasticity were inconclusive (2 RCTs; SMD = 0.930, 95% CI [−0.179, 2.039], p = 0.100). Subgroup analysis suggested greater hydration benefits with interventions ≥ 8 weeks, though these exploratory findings require cautious interpretation. No serious adverse events were reported. GRADE certainty ranged from very low to moderate. Conclusions Oral probiotic supplementation may be associated with skin hydration and barrier function improvement in healthy adults with low‐to‐moderate certainty evidence. Effects are most consistent for TEWL reduction. High heterogeneity, limited numbers of outcome‐specific trials, frequent industry sponsorship, and potential publication bias warrant cautious interpretation. Future large‐scale RCTs with standardized strains, dosing, and long‐term follow‐up are needed.