Abstract

Objectives: To evaluate whether a single immediate, sub-purpuric vascular pass at the resurfacing visit shortens post-laser erythema versus deferring treatment until day 14, and to compare efficacy between 595-nm PDL and 577-nm yellow laser. The primary endpoint was the between-side Erythema Index (EI) at day 14. Secondary outcomes included EI at day 28 and week 8, persistent-erythema rates, patient-reported redness bother, and safety, plus interaction with initial post-CO₂ EI. The design prioritized meaningful early recovery gains to reduce downtime. Introduction: Post-laser erythema (PLE) after fractional ablative CO₂ resurfacing prolongs downtime and may heighten PIH risk. Vascular-selective lasers can hasten clearance, yet the optimal timing and wavelength remain unsettled. We conducted a prospective, two-arm, split-face comparison of 595-nm pulsed dye laser (PDL) and 577-nm yellow HOPSL. Each subject received an immediate, low-fluence pass on the right at the resurfacing visit and a delayed, standard-fluence pass on the left. Recovery was tracked via serial Mexameter Erythema Index measurements. Materials / method: Prospective, evaluator-blinded split-face trial in 36 adults with moderate atrophic acne scars. All received standardized fractional ablative CO₂ to both cheeks. Randomized 18 to PDL and 18 to 577-nm HOPSL. In each arm: right cheek immediate low-fluence day 0; left cheek standard non-purpuric day 14. PDL: 10 mm, 3–4 J/cm² (day 0); 7–8 J/cm² (day 14). 577-nm: 6 mm, 4–5 J/cm² (day 0); 12–16 J/cm² (day 14). EI at baseline, post-CO₂, day 14, day 28, week 8; mixed-effects analyses. Safety and PIH monitored; photoprotection mandated. Results: At baseline, EI averaged ~250; post-CO₂ it spiked to ~600 bilaterally. Day 14: immediate PDL reduced EI to ~310 vs 380 with delayed; immediate 577-nm reduced EI to ~290 vs 370 delayed. Persistent erythema was lower with immediate use (PDL 11% vs 39%; 577-nm 6% vs 33%). By day 28, after delayed sides received their first treatment, values converged: PDL 260 vs 270; 577-nm 245 vs 255. At week 8, all groups approached baseline (PDL 248 vs 250; 577-nm 246 vs 249). Greater benefit was seen in patients with higher immediate post-CO₂ EI. Safety profile was favorable, with only rare transient purpura Conclusion: Immediate low-fluence vascular treatment integrated at the time of CO₂ resurfacing significantly accelerated erythema recovery at day 14, with both lasers effective. The 577-nm yellow laser showed a slightly stronger reduction than PDL in the early phase, but by day 28 values converged after delayed therapy, and by week 8 all cheeks normalized. Patients with higher initial erythema gained the most from immediate intervention. The approach was safe, well-tolerated, and reduced patient-reported bother. Immediate passes can shorten downtime, while a day-14 session remains a safe fallback