High-energy versus low-energy fractional CO₂ laser in the treatment of hypertrophic scars: A comparative review of efficacy, safety, and tissue remodeling

Fractional CO 2 laser therapy has become a cornerstone in the management of hypertrophic scars due to its ability to promote dermal remodeling through controlled thermal injury. However, there is ongoing debate regarding the ideal laser energy parameters that balance efficacy with safety. This review synthesizes clinical data from studies published between 2005 and 2025 that utilized ablative fractional CO 2 laser (ablative fractional resurfacing [AFR]) for hypertrophic scars, comparing outcomes between high-energy protocols (≥30 mJ/microthermal zone [MTZ]) and low-energy protocols (≤20 mJ/MTZ). High-energy settings demonstrated superior short-term clinical efficacy, with significant reductions in scar thickness, erythema, and stiffness often observed within fewer treatment sessions. These outcomes were corroborated by histopathological findings, showing deeper collagen remodeling and increased neocollagenesis. However, these benefits were offset by increased risk of side effects such as prolonged post-treatment erythema, edema, pain, and post-inflammatory hyperpigmentation, especially in patients with Fitzpatrick skin types IVVI. Low-energy settings, while requiring more sessions to achieve comparable improvements, were associated with fewer adverse effects and greater patient comfort, with histologic evidence of gradual, superficial dermal remodeling. Patient satisfaction was generally higher when treatment was personalized based on scar characteristics, anatomical site, skin phototype, and individual tolerance. Notably, high-energy protocols were more suitable for mature, thick scars located on less pigment-sensitive areas, whereas low-energy settings were preferable for recent or facial scars, or those in darker skin tones. The review underscores the importance of individualized treatment planning and suggests that energy modulation should be guided by a comprehensive assessment of scar morphology and patient-specific factors. Overall, both high- and low-energy AFR protocols are effective, but strategic personalization is critical to optimizing therapeutic outcomes while minimizing treatment-related risks.