Cosmetic Efficacy and Sustainability of Beer and Brewing By-Products in Skin Care: A Formulation-Driven In Vitro and In Vivo Evaluation

The brewing process generates substantial by-products rich in potentially bioactive compounds (e.g., polyphenols and fermentation metabolites), providing a sustainable and appealing source of cosmetic ingredients. Oil-in-water (O/W) emulsions containing 20% (w/w) aqueous extracts from Bionda Triplo Malto beer, wort, and key brewing by-products (hops, yeast, and spent grain) were developed and evaluated using a combined in vitro–in vivo approach. Aqueous extracts were first screened on human immortalized dermal fibroblasts (BJ-5ta) at 0.25–1 mg/mL for cytocompatibility and antioxidant activity. Within this concentration range, no significant changes in cell viability or intracellular antioxidant capacity under UV stress were detected, suggesting cytocompatibility but limited inherent activity. When incorporated into O/W emulsions and tested at an active-equivalent concentration of 10 mg/mL, the formulations increased fibroblast metabolic activity and antioxidant response. In contrast, free extracts at 10 mg/mL showed concentration-dependent cytotoxicity for some matrices, with beer- and yeast-based emulsions demonstrating the strongest effects. The emulsions exhibited good physicochemical stability (pH ~5.7–6.2; viscosity 4750–5150 mPa·s), passed the ISO 11930:2012 challenge test, and were well tolerated in patch testing. In a double-blind, randomized split-forearm study on 50 healthy volunteers over 30 days, beer, yeast, and spent grain-based formulations improved skin parameters versus baseline. TEWL decreased (e.g., beer: 16.22 ± 5.12 to 10.77 ± 2.22 mg·m−2·h−1; yeast: 16.29 ± 5.66 to 10.18 ± 1.08; spent grain: 14.45 ± 4.34 to 11.66 ± 2.28), hydration increased (beer: 35.15 ± 5.93 to 42.26 ± 3.78; yeast: 33.27 ± 4.87 to 42.92 ± 2.48; spent grain: 34.22 ± 5.19 to 41.16 ± 3.17, and elasticity improved for beer and yeast formulations (62.33 ± 3.27 to 70.24 ± 2.12 N/m) and yeast (61.21 ± 4.72 to 72.13 ± 5.55 N/m). Based on these findings, brewing-derived ingredients demonstrate potential as cosmetic actives, with formulation critically determining their clinical efficacy.