Oral Collagen Supplementation for Skin Hydration and Elasticity: A Systematic Review and Meta-Analysis

Background: Oral collagen supplements are widely used as nutricosmetics for skin ageing; however, the magnitude and reliability of their effects remain uncertain because of methodological heterogeneity and potential bias. Methods: We conducted a systematic review and random-effects meta-analysis in accordance with PRISMA 2020 and was registered in PROSPERO (CRD420261285731). PubMed/MEDLINE, Embase, Scopus, Web of Science, and Cochrane CENTRAL were searched from database inception to 1 January 2026. Randomized controlled trials comparing oral hydrolysed collagen or collagen peptides with placebo or no treatment in adults were eligible. Risk of bias was assessed independently by two reviewers using Cochrane RoB 2. Results: Fifteen randomized controlled trials were included. Quantitative synthesis was possible for five trials reporting skin hydration and four reporting skin elasticity. Oral collagen supplementation improved skin hydration (standardized mean difference [SMD] 0.71; 95% confidence interval [CI] 0.08 to 1.34; p = 0.027; I2 = 90.4%) and elasticity (SMD 0.78; 95% CI 0.12 to 1.45; p = 0.022; I2 = 88.9%). Sensitivity analyses excluding a high-leverage multi-ingredient trial attenuated the estimates, particularly for elasticity. Most trials raised some concerns regarding bias, mainly because allocation concealment, prespecified outcome selection, or complete statistical reporting was insufficiently described. Conclusions: Oral collagen supplementation may improve instrumental measures of skin hydration and elasticity, but the certainty and clinical interpretation of these effects are limited by substantial heterogeneity, short follow-up, incomplete reporting, and frequent industry involvement.