Efficacy and safety of a novel anhydrous 0.1% retinal and 10% azelaic acid concentrate for blemish-prone skin: An eight-week randomized prospective split-face, vehicle-controlled study.

BACKGROUND: Blemish-prone skin is driven by follicular hyperkeratinization, excessive sebum production, microbial dysbiosis and inflammation, often accompanied by post-inflammatory erythema and hyperpigmentation. Retinal and azelaic acid are established topical actives with complementary mechanisms of action, yet no clinical study has evaluated their combination in a single formulation. OBJECTIVE: To evaluate the efficacy and tolerability of a minimalist anhydrous concentrate combining retinal (0.1%) and azelaic acid (10%) in improving objective and self-perceived features of blemish-prone skin over 8 weeks. METHODS: In a prospective randomized, vehicle-controlled split-face study, participants applied the active concentrate to one side of the face and a vehicle concentrate to the contralateral side, mixed with a moisturizer immediately before application. Assessments were performed at baseline and week 8 using standardized photography, Antera 3D imaging and consumer questionnaires. Statistical comparisons were performed within subjects and between treatment conditions. RESULTS: Twenty-three participants completed the study (age 16-49 years; mean 28 years; Fitzpatrick skin types I-IV). After 8 weeks, the active formulation demonstrated statistically significant improvements versus baseline and vehicle. Skin texture improved by 10.9% versus baseline (p < 0.0001) and 5.6% versus vehicle (p = 0.0016). Skin volume (surface irregularities/pits) decreased by 24.8% versus baseline (p < 0.0001) and 12.7% versus vehicle (p = 0.0053). Overall redness was reduced by 13.2% versus baseline (p = 0.0009) and 18.1% versus vehicle (p = 0.011), while maximum redness intensity decreased by 8.8% versus baseline (p < 0.0001) and 5.2% versus vehicle (p = 0.029). The pore parameter showed a 22.3% improvement versus vehicle (p = 0.015) and 15.9% versus baseline (p = 0.051). Self-assessments indicated improvements in overall skin condition (87%), pimple size/severity (78%), number of pimples (74%), calmer skin feel (95%) and reduced oiliness (82%). Visible improvements within 4 weeks were reported by 65% of participants. Adverse events were few, mild and transient. CONCLUSION: An anhydrous six-ingredient concentrate combining retinal 0.1% and azelaic acid 10% significantly improved texture, surface irregularities, redness and pore appearance in acne-prone skin over 8 weeks with good tolerability. The formulation provides a stability-optimized approach for combining two evidence-based actives in a minimalist system.