Both ablative and nonablative fractional devices can improve the severity of acne scarring, but there are significant differences in risk factors and recovery, according to Michal Wen Sheue Ong, MD, of King’s College Hospital in London. In “Fractional Laser Resurfacing for Acne Scars: A Review” (British Journal of Dermatology, accepted for publication, Feb. 2012), Ong investigates the results of 26 clinical studies—13 on fractional ablative devices; 13 on fractional nonablative devices—published between 2003 and 2011. He reports that, even when allowing for methodological variability between the studies, ablative devices create an improvement in acne scars of 26% to 83% versus an improvement range of 26% to 50% for nonablative lasers. In terms of recovery, patients who received ablative treatments experienced three to 14 days of erythema, while patients who underwent nonablative resurfacing experienced one to three days of erythema. Up to 92.3% of fractional ablative patients experienced post-inflammatory hyperpigmentation (PIH) for a maximum duration of six months. Only 13% of nonablative patients experienced PIH, which lasted up to a week. According to Ong, four of the studies reviewed were split face, randomized, controlled studies; a small number utilized 3D Optical Profiling Imaging and histology for objective assessment; and the outcomes of the studies included both subjective and objective assessments of improvement.