Microneedling for Post-Acne Scars: Dose-Response Analysis

Abstract

Introduction: Microneedling induces collagen remodeling without epidermal ablation. This review examines optimal needle depth and session number for atrophic acne scars. Methods: Twelve prospective studies (n=412) using standardized microneedling protocols. Needle depths ranged 0.5–2.5 mm; sessions 1–6. Outcome: qualitative scar improvement scale (0-4). Results: Depth ≥1.5 mm gave superior improvement (mean score 2.8 vs 1.6 for <1.5 mm, p<0.001). Four sessions produced maximal benefit (69% moderate-to-good improvement); additional sessions yielded diminishing returns. Adverse events: mild erythema (100%), transient post-inflammatory hyperpigmentation (8% in skin types V-VI). Discussion: Penetration to reticular dermis is necessary for neocollagenesis. Darker skin requires lower depths and pre-treatment with hydroquinone to avoid PIH. Conclusions: Four sessions of 1.5–2.0 mm depth at 4-week intervals is optimal for atrophic scars.