Laser therapy for burn scars (CO2, pulsed dye, fractional)

Overview

Laser therapy is the modality that fills the gap between conservative scar management and operative scar revision. Pressure garments and silicone sheets carry the conservative burden in mature hypertrophic scars; surgical revision, contracture release, and flap reconstruction address contour and joint function in the operative phase; laser therapy targets the cellular and microvascular character of the scar itself, addressing stiffness, texture, vascularity, pigmentation, pruritus, and pain in an outpatient setting ^[1][7][22].

The clinical reality across burn centers is that hypertrophic burn scars are common, symptomatic, and durable. They are uncomfortable; they itch; they limit motion across joints; they pull at facial expressions; and they remain visible on exposed surfaces. The evidence base over the last decade has consolidated on ablative fractional CO2 laser as the workhorse modality for established hypertrophic scars and pulsed dye laser as the modality of choice for erythema and pruritus, with a growing role for laser-assisted drug delivery using intralesional corticosteroid or 5-fluorouracil ^{[1][2][12][22][29][30]}. The Hultman cohort of 147 patients across 415 sessions paired pulsed dye laser for pruritus and erythema with fractional CO2 for stiffness and texture and documented a Vancouver Scar Scale drop from 10.4 to 5.2 and a UNC Scar Scale drop from 5.4 to 2.1 (both P < 0.0001), establishing the combination-by-feature approach that most burn centers now use ^[22]. The strongest controlled evidence for PDL is on pruritus reduction; objective scar-scale endpoints have shown mixed signals across the controlled literature, including null findings on Vancouver score, photographic assessment, and surface profile in the only within-patient-control PDL RCT ^[7].

Laser therapy does not replace pressure, silicone, surgical release, or skin grafting; it complements them. Conservative scar management still has a primary role, particularly for keloid-prone scars where silicone gel sheeting and intralesional corticosteroids carry the strongest evidence-based recommendations ^[37]. Laser therapy enters when scar maturation has produced fixed hypertrophic features that conservative care alone has not resolved, or when symptomatic erythema and pruritus persist during the maturation phase. Laser therapy of skin in the German S2k guideline includes hypertrophic, keloidal, and burn or scald scars among recognized indications ^[36].

Pathophysiology

The cellular target of laser therapy on burn scar is the dysregulated fibroblast in a vascularized, collagen-rich scar matrix. Different wavelengths address different elements of this matrix. The 585 nm and 595 nm pulsed dye lasers target oxyhemoglobin in scar microvasculature; the original rationale for PDL in hypertrophic scar was extrapolation from port-wine-stain treatment, although blood vessel diameters in hypertrophic scar tissue are much smaller than the vessels in port wine stains for which the laser was designed ^[7]. The 10,600 nm fractional ablative CO2 laser produces histopathologically-evident collagen remodeling in hypertrophic burn scar, with significant reduction in scar thickness and in upper-dermal collagen bundle thickness and density ^[38].

Histological evidence supports a real mechanism rather than a cosmetic effect at the surface. After PDL treatment of hypertrophic burn scars, biopsy specimens showed a normal number of dermal fibroblasts with decreased sclerosis ^[24]. After non-ablative fractional laser treatment of mature burn scars, scar appearance improved (P < 0.001 versus untreated) and histology at 6 months supported collagen remodeling ^[33]. After fractional CO2 ablative treatment, histopathology revealed significant decrease in scar thickness in hypertrophic scars (P < 0.001) along with a significant decrease in collagen bundle thickness and density in the upper dermis; this histological signal corresponded with clinical improvement on Vancouver and POSAS scales ^[38]. The ELIPSE prospective randomized controlled trial extended the mechanistic case by performing RNA sequencing on laser-treated and control scars and showing that fractional CO2 laser induced sustained changes in fibroblast gene expression for at least 3 months after treatment, although the trial found no significant difference in VSS, scar erythema, or pigmentation between treated and control scars on its clinical primary endpoint ^[18].

Density and energy each contribute independently to histological remodeling. In a randomized trial of high- versus low-density fractional CO2 laser in hypertrophic post-burn scars, histopathological evaluation revealed a significant drop in the mean area percent of collagen in the three parameter sets, with greatest improvement at high density (P < 0.001) ^[25]. In a pediatric study of energy and density combinations, the increase of density showed the therapeutic effect earlier than the increase of energy ^[26].

Classification

Laser modalities for burn scar fall into four functional classes. The boundaries are not rigid (a single patient often receives more than one modality across treatment sessions), but the functional classification organizes selection at the treatment table.

Ablative fractional lasers (AFL). The 10,600 nm fractional CO2 laser is the dominant member of this class and the modality with the strongest meta-analytic evidence for burn scar ^[1][2][3][4]. The 2940 nm erbium YAG fractional laser is the alternative ablative wavelength, with the advantage of less surrounding thermal injury and faster healing per session, used increasingly for laser-assisted drug delivery ^[30]. Ablative fractional lasers address stiffness, contour, and abnormal texture; they are the workhorse for established hypertrophic burn scar ^[22].

Non-ablative fractional lasers (NAFL). Wavelengths around 1540 to 1550 nm create columns of thermal injury without surface ablation. The 2015 randomized trial of non-ablative fractional laser on mature burn scars showed improvement in scar appearance (P < 0.001 versus untreated) with patient-rated POSAS dropping from 7 to 4 at 6 months ^[33]. Non-ablative fractional therapy has a lower side-effect profile than ablative fractional and is the preferred choice when ablation is not tolerable ^[23][33].

Vascular lasers (pulsed dye laser and Nd:YAG). The 585 nm and 595 nm pulsed dye lasers target microvasculature and are the strongest evidence for erythema and pruritus reduction ^[7][20]. The Nd:YAG laser at 1064 nm reaches deeper vascular targets; the meta-analysis of Nd:YAG laser for keloid and hypertrophic scars showed a VSS reduction of 2.96 (95% CI 2.08–3.84, P < 0.01), with a more marked effect on hypertrophic scars than on keloid scars ^[10].

Photobiomodulation and low-level laser therapy. Sub-thermal-injury light-tissue interactions used for wound healing and pruritus modulation ^[20]. Photobiomodulation is a different mechanistic category from ablative or vascular laser and is not the primary intervention for established hypertrophic burn scar; the evidence base for its role in scar reduction remains thin compared with the AFL and PDL evidence bases ^[6][9].

Assessment

Scar selection drives laser selection. The reconstructive question for a candidate burn scar has four parts: what is the dominant clinical feature, what is the scar maturity, what is the patient's skin phototype, and what conservative care has already been tried.

The dominant clinical feature anchors laser type. Pruritus and erythema in an immature, vascular scar argue for pulsed dye laser ^[7][20][24]. Stiffness, abnormal texture, and contour argue for ablative fractional CO2 ^[1][2][22]. Mixed features in the same patient (a common pattern in extensive burn) argue for combination therapy across sessions ^[22]. The Hultman 2013 cohort used pulsed dye laser at 327 of 415 sessions for pruritus and erythema and fractional CO2 at 139 sessions for stiffness and abnormal texture in the same patient population ^[22].

Scar maturity influences the choice between non-ablative and ablative approaches. The systematic review and meta-analysis of scar age, laser type, and treatment interval in adult burn scars found that vascularity improvement was greater when laser therapy was performed more than 12 months after injury than less than 12 months after injury, with the same pattern for scar height; pulsed dye laser gave the greatest reduction in VSS/POSAS scores compared with non-ablative and ablative lasers in the pooled data ^[8]. A randomized trial of non-ablative fractional photothermolysis in linear surgical hypertrophic scars (a related but distinct scar population) showed that younger scars respond better to non-ablative fractional remodeling ^[23]. The fractional CO2 prospective evaluation found that improvement in thickness, texture, color, and symptoms after CO2 ablative fractional treatment was equally significant irrespective of scar maturation status, in patients ranging up to 23 years after injury ^[34].

Patient skin phototype influences risk of post-inflammatory hyperpigmentation, particularly for ablative wavelengths. The fractional ablative laser-assisted drug delivery cohort that included Fitzpatrick skin type IV to VI patients reported that age, gender, Fitzpatrick skin type, scar age, and ethnicity did not predict responder grouping, but melanin index analysis confirmed that laser-assisted drug delivery led to improvements in hyperpigmentation in selected patients ^[27]. The literature on parameter selection for Fitzpatrick IV to VI burn scar is thin; lower-density parameters produced fewer adverse events in the Lin/Anderson NAFR trial in linear surgical hypertrophic scars ^[23].

Conservative care comes before laser. Pressure garments and silicone sheets carry primary-role evidence for hypertrophic scar prevention and management ^[37], and laser entry is typically after conservative measures have plateaued or after established hypertrophic features make conservative care inadequate.

Management

Fractional CO2 laser for established hypertrophic burn scar

Ablative fractional CO2 laser is the most-studied laser intervention for hypertrophic burn scar and the modality with the strongest aggregate evidence. The 2021 meta-analysis of fractional CO2 laser therapy in burn scars showed significant improvement in the Vancouver Scar Scale (WMD -3.24, 95% CI -4.30 to -2.18, P < 0.001), POSAS patient (WMD -14.05, P = 0.001), POSAS observer (WMD -6.31, P < 0.001), and ultrasound-measured scar thickness (WMD -0.54, P < 0.001) ^[1]. A second 2021 meta-analysis of 14 studies converged on the same direction: VSS MD -3.01, POSAS patient MD -14.38, POSAS observer MD -8.81, with improvement particularly in pigmentation, vascularity, pliability, and scar height, plus reductions in pain and pruritus ^[2]. The 2021 systematic review and meta-analysis using only the VSS as outcome pooled 282 patients across 8 studies and found an average VSS improvement of 29% following fractional CO2 ablative laser treatment ^[3]. A third 2021 systematic review and meta-analysis reported similar direction with statistically significant improvements in scar profiles and few reports of adverse effects ^[4]. The collective signal across these four meta-analyses is consistent: fractional CO2 reduces validated scar-scale scores and reduces ultrasound-measured scar thickness, with mild and tolerable adverse events.

Prospective cohort data add depth to the meta-analytic signal. The 2017 prospective evaluation of 47 patients with 118 burn scars showed that at a median of 55 days after CO2 ablative fractional treatment, intra-patient normalized scar thickness decreased from a median of 2.4 mm to 1.9 mm (P < 0.001), overall POSAS patient scale decreased from 9 to 5 (P < 0.001), pain and pruritus showed significant reduction, and quality of life increased significantly by 15 points (P < 0.001), with improvement equally significant in mature scars up to 23 years after injury and in immature scars ^[34]. The 2016 prospective evaluation of 80 scars (48 treatment, 32 control) showed objectively measured improvements in thickness, sensation, erythema, and pigmentation in treated scars (P = 0.001 to 0.004) ^[35].

The single most consequential nuance for technique is density. The randomized trial of high- versus low-density fractional CO2 laser in hypertrophic post-burn scars showed that high-density parameters produced significantly higher VSS and POSAS improvement (P < 0.001) and significantly greater histological reduction in collagen area percent ^[25]. The pediatric energy-and-density analysis converged on the principle that increasing density produced earlier and greater therapeutic effect than increasing energy, with the trade-off that higher density also increases procedural pain ^[26]. The best parameter combination in that pediatric study was 17.5 mJ at 10 percent density ^[26].

Pulsed dye laser for vascular and symptomatic immature scar

Pulsed dye laser at 585 or 595 nm is the modality of choice for erythematous, vascularized hypertrophic burn scar with prominent pruritus and pain. The 2003 randomized controlled trial of 585 nm pulsed dye laser in burn scars showed that pruritus improved significantly between treatment and control areas (P < 0.001), although Vancouver scores did not differ significantly between treatment and control at 6 (P = 0.876) or 12 months (P = 0.680); the authors concluded that the 585 nm flashlamp-pumped pulsed dye laser is an effective treatment for the intense pruritus often experienced during the healing process after a burn injury ^[7]. The evidence-based review of post-burn pruritus identified pulsed dye laser as the best-quality non-pharmacological treatment for post-burn pruritus ^[20]. The 1998 series of 16 patients with 40 hypertrophic burn scars treated with 585 nm PDL reported symptomatic improvement after one treatment, decreased erythema and improved texture and pliability after an average of 2.5 treatments, normal numbers of dermal fibroblasts with decreased sclerosis on histology, and effective improvement in pliability, texture, and erythema with cosmetically and functionally acceptable results ^[24].

The 2025 ELABS randomized controlled trial of early pulsed dye laser plus standard care versus standard care alone for hypertrophic burn scars showed a statistically significant improvement in patient-rated scar quality (P = 0.041) and in patient-perceived change in scar quality (P = 0.01) at six months, with no significant differences in quality-of-life, observer-rated POSAS, or colour measurement; the intervention had no unexpected adverse events, although early PDL was not cost-effective at the £20,000 per QALY willingness-to-pay threshold at six months ^[19]. The authors observed that scar maturation is prolonged and dynamic, and longer-term follow-up of up to two years is required to understand the eventual clinical effect ^[19]. The pediatric multimodal analysis of early pulsed-dye laser plus compression versus compression alone showed less scar erythema, less scar height, and greater tissue elasticity after two to three PDL-plus-compression treatments than with compression alone, with VSS scores improving more on vascularity, pliability, pigmentation, and height in the combination group ^[21].

Combination therapy and feature-targeted use

Combining laser modalities targets multiple scar features in the same patient. The 2024 single-blinded randomized controlled trial of CO2 fractional laser in combination with pulsed dye laser versus each alone in hypertrophic burn scars showed significant improvement in VSS, scar color, vascular bed, height, and pliability in all groups, with directionally greater improvement in each measure in the combination group; the authors noted that the superiority of the combined group did not reach statistical significance but framed the magnitude of improvement as clinically significant, with the most pronounced effect in immature scars ^[12]. The 2025 systematic review of pulsed dye laser, fractional CO2, or combination for burn scar treatment showed that PDL was associated with significantly greater reduction in total VSS than combination therapy (MD -0.90), while AFCL showed no significant difference; qualitative synthesis reported consistent improvements in scar appearance, texture, pain, and pruritus across studies, with good safety profiles ^[11]. The 2025 pediatric systematic review of PDL combined with ablative fractional CO2 reported significant improvement in VSS and POSAS scores using lower laser energy, higher density parameters, and shortened treatment intervals (less than 1 month), with the combination superior to single-modality laser ^[13].

Laser-assisted drug delivery (LADD)

Ablative fractional laser channels deliver topical and intralesional drugs into the deep scar; a hybrid intervention pairing this topic with intralesional injection therapy (cross-leaf attribution; see also [[intralesional-injection-hypertrophic-scar-keloid]]). Three 2025 randomized controlled trials of laser-assisted drug delivery converge on the same direction: pairing ablative fractional laser (CO2 or Er:YAG) with intralesional triamcinolone or 5-fluorouracil produces greater scar-scale improvement than laser monotherapy on validated endpoints, with no clear superiority between triamcinolone and 5-fluorouracil ^[28][29][30]. The 2025 randomized controlled trial of fractional CO2 laser with or without triamcinolone acetonide or 5-fluorouracil in early postburn hypertrophic scars showed that all groups achieved significant improvement in overall scar severity and height (P < 0.05); the triamcinolone-plus-laser group showed significant improvement in pliability, height, and pigmentation; the 5-FU-plus-laser group showed significant reductions in vascularity, pliability, and height; the trial found no statistically significant difference in efficacy between 5-FU and triamcinolone added to laser, suggesting that neither agent offers superior efficacy over the other ^[28]. The 2025 study of 5-FU combined with ultra-pulsed fractional CO2 laser showed greater improvement in VSS and PSAS scores than laser alone, a total effective rate of 93.33% in the combination arm, and lower adverse-reaction incidence (6.67%) than laser alone ^[29]. The 2025 double-blind randomized split-scar trial of Er:YAG laser plus intralesional triamcinolone versus Er:YAG alone in post-burn scars showed 52.9% of combination-arm scars achieved more than 75% reduction in thickness versus 26.5% in the laser-alone arm (P < 0.05), with better symptomatic relief for pruritus, paraesthesia, and pliability and a better safety profile ^[30].

Treatment of post-burn pruritus

Beyond PDL (whose pruritus evidence is described in the PDL sub-section above), high-intensity laser therapy adds an adjuvant pathway. The 2017 double-blind randomized study of pulsed high-intensity laser therapy versus placebo laser plus cetirizine in post-burn pruritus showed that the active laser group had significant reductions in itch severity score, improvements in quality of life and visual analog pain score, improved hand grip strength, and decreased cetirizine intake at 6 weeks and 12 weeks, suggesting that HILT combined with cetirizine is more effective than placebo laser with cetirizine ^[31]. The 2024 systematic review and meta-analysis of post-burn pruritus treatment concluded that current modalities produce a statistically significant but not clinically significant reduction in pruritus, framing the gap between trial signal and bedside meaningfulness in this symptom domain ^[32].

Complications

The complication signature of laser therapy in burn scar concentrates in transient erythema and edema, post-inflammatory hyperpigmentation, vesicles, herpes simplex reactivation, and acneiform eruption. The 2021 meta-analysis of fractional CO2 in burn scars characterized side effects and complications as mild and tolerable ^[1]. The 2021 systematic review of ablative fractional laser for hypertrophic burn and traumatic scars characterized adverse events as generally infrequent and minor across 23 evaluated studies ^[5]. The 2025 systematic review of PDL, fractional CO2, or combination therapy for burn scar treatment characterized safety profiles as good with high patient satisfaction ^[11]. The 2024 pediatric meta-analysis of fractional CO2 reported erythema and vesicles as the most common complications, with an incidence of 4.09% ^[16]. The 2016 prospective evaluation of FCO2 in mature burn scars characterized treatment-session pain with a score averaging 4.7/10 during treatment and 2.4/10 five minutes after ^[35].

Density and energy modulate adverse-event severity. The randomized trial of high- versus low-density fractional non-ablative laser found that the side-effect profile was more severe in the high-density-treatment arm, with three subjects rating their scars as worse at the end of the study; the authors concluded that low-density treatment is at least as effective with fewer side effects ^[23]. Lower density produced fewer adverse events in the Lin/Anderson NAFR trial in linear surgical hypertrophic scars ^[23]; the literature on interval modulation for sensitive locations (face, neck) and higher Fitzpatrick types in burn scar is thin, with parameters drawn from individual case series ^[25][27].

Post-inflammatory hyperpigmentation, herpes simplex eruption, and acneiform eruption are the documented adverse events in the 2017 prospective study of fractional microplasma radiofrequency for non-hypertrophic post-burn scars in Asian patients; severe events such as acute infection, hypertrophic scarring, or depigmentation were not observed ^[39]. The 2025 ELABS PDL trial reported no unexpected adverse events related to the intervention ^[19]. The 2003 PDL burn scar trial reported that one patient withdrew because of scar breakdown and three additional patients were lost to follow-up among 38 patients enrolled across four age and scar-maturity groups ^[7].

Laser-assisted drug delivery can drive hyperpigmentation improvement in selected patients; the 2023 fractional laser scar revision cohort with LADD showed that based on melanin index values, fractional laser scar revision led to improvements in hyperpigmentation in certain patients, and age, gender, Fitzpatrick skin type, scar age, ethnicity, or type of drug delivered did not predict responder grouping ^[27].

Special Considerations

Pediatric burn scar

Laser therapy in pediatric hypertrophic burn scar is well-tolerated and effective on the same scar-scale measures used in adult studies. The 2024 systematic review of procedural treatments for burn scars in 256 children documented satisfactory outcomes across modalities; in the laser-treatment subgroup of 161 children, VSS reductions ranged from 55.55% to 76.31%, with outcomes rated good (24.61%) to excellent (60%), and laser treatment using local anaesthesia was well tolerated; light-based therapies and lasers may serve as effective and tolerable options for scar treatment in this age group, often eliminating the need for general anaesthesia ^[17]. The 2019 prospective evaluation of 49 pediatric patients across 180 laser sessions of CO2-AFL showed statistically significant improvement in observer-rated POSAS pigment, thickness, relief, pliability, and surface area after one treatment, with continued improvement until the last session; total POSAS dropped from 89.6 ± 17.5 to 76.6 ± 16.8 (P < 0.0001) after the first treatment and further to 69.2 ± 14.9 (P < 0.0001) at final session ^[14]. The 2023 10-year single-institution pediatric experience confirmed statistically significant improvement in elasticity after each laser treatment and a correlation between the number of sessions and elasticity gain; 96% of patients or parents were satisfied with the laser therapy and 90% wished to repeat the procedure ^[15].

The 2024 meta-analysis of CO2 fractional laser in pediatric post-burn hypertrophic scar reported that CO2 fractional laser was beneficial to recovery of hypertrophic burn scar in children with effective improvement in scar symptoms and signs and acceptable adverse-event profile (erythema and vesicles in 4.09%) ^[16]. The 2025 systematic review of PDL combined with AFCL in pediatric post-burn scar showed that the combination significantly improved VSS and POSAS scores and was superior to single-type laser therapy when used with lower laser energy, increased density, and shortened intervals; rash was the most common complication ^[13]. The 2012 multimodal analysis of early PDL plus compression in pediatric scars showed less erythema and height and greater tissue elasticity than with compression alone after two to three treatments ^[21].

Treatment timing and scar maturity

Whether to treat immature or mature scars is a recurring question. The 2023 systematic review and meta-analysis of scar age, laser type, and treatment interval showed that vascularity improvement was greater when laser therapy was performed more than 12 months after injury (-1.50; 95% CI -2.58 to -0.42; P = 0.01) than less than 12 months after injury (-0.39; 95% CI -0.68 to -0.10; P = 0.01), with the same pattern for scar height ^[8]. The 2011 NAFR randomized trial in linear surgical hypertrophic scars suggested that younger scars respond better to non-ablative fractional remodeling, supporting early intervention in that scar population ^[23]. The 2017 prospective FCO2 evaluation found that improvement was equally significant irrespective of scar maturation status, in scars up to 23 years after injury ^[34]. The 2025 ELABS trial of early PDL showed patient-rated scar quality improvement at six months while emphasizing that longer follow-up (up to two years) is required to understand eventual clinical effect ^[19]. The 2023 ELIPSE prospective RCT of CO2 ablative fractional treatment of burn-related scarring found no significant difference in VSS, scar erythema, or pigmentation between treated and control scars; patient POSAS improved in scar thickness and texture; AFCO2L-treated scars were rated better than controls by blinded raters; and RNA sequencing suggested the laser alters the fibroblast transcriptome for at least 3 months after treatment ^[18].

The composite signal across these trials is that both immature and mature hypertrophic scars respond, but the dominant feature (vascular/erythematous in immature scar; stiffness/contour in mature scar) drives the choice of modality.

Special anatomic regions and scar phenotypes

Face, neck, hand, and joint-overlying scars carry the highest functional and aesthetic stakes. Single-modality laser therapy may not match the depth of revision needed; combination with intralesional drug delivery, pressure therapy, or surgical revision may be necessary ^[12][30]. Keloid scar (versus hypertrophic scar) is a separate phenotype: the Nd:YAG laser meta-analysis showed a less marked effect on keloid scars (MD 2.02; 95% CI 0.58 to 4.63; P = 0.10) than on hypertrophic scars (MD 3.05; 95% CI 1.58 to 4.52; P < 0.01); the combination of Nd:YAG with other treatment methods produced a more significant change in VSS score (MD 4.28; 95% CI 2.07 to 6.49) ^[10]. The 2015 open-label controlled study of ablative CO2 fractional resurfacing in thermal burn scars showed textural improvement and significant decrease in Vancouver, POSAS observer, and POSAS patient scores in hypertrophic burn scars but not in keloidal scars (P = 0.011, 0.017, and 0.018 in hypertrophic only) ^[38].

Outcomes

Validated scar scales and patient-reported symptoms are the outcome endpoints across the burn-scar laser literature. The convergent direction across the FCO2 burn-scar meta-analyses is consistent: VSS improvement of approximately 3 points (WMD -3.24 in ^[1]; MD -3.01 in ^[2]) and POSAS patient and observer improvements of 14 and 6 to 9 points respectively, with significant reductions in pain and pruritus and in ultrasound-measured scar thickness ^[1][2][3]. The 2021 ablative fractional laser systematic review reported that 22 of 23 evaluated studies documented statistically significant or meaningful qualitative improvements in nearly all outcome measures, although heterogeneity precluded meta-analysis of pooled data ^[5]. The 2017 systematic review of laser therapy for hypertrophic burn scar reported improvements in scar symptoms following laser treatment in 11 of 12 included studies, with the caveat that overall quality and risk of bias were issues across all studies ^[6].

The strongest controlled outcome data come from the Hultman 2013 cohort: paired pulsed dye laser for pruritus and erythema and fractional CO2 for stiffness and abnormal texture produced VSS reductions from 10.4 (SD 2.4) to 5.2 (1.9) (P < 0.0001) and UNC Scar Scale reductions from 5.4 (2.5) to 2.1 (1.7) (P < 0.0001), establishing the laser-by-feature treatment pattern that is now widely adopted in burn centers ^[22]. The Anderson 2011 RCT of non-ablative fractional photothermolysis in linear surgical hypertrophic scars (a related but distinct scar population) demonstrated efficacy with 17 of 20 patients reporting improvement; low-density treatment was at least as effective as high-density with fewer side effects; and younger scars responded better, with the conclusion that early intervention may be a key approach for hypertrophic scar ^[23]. The 2017 prospective AFCO2 evaluation showed quality-of-life increase of 15 points (P < 0.001) alongside the scar-scale and ultrasound-thickness improvements, evidence that the symptom-domain improvements translate to patient-reported function ^[34].

Combination therapy outperforms monotherapy on most scar features. The 2024 single-blinded RCT of CO2 fractional plus PDL versus each alone in hypertrophic burn scars showed significant improvement in VSS, scar color, vascular bed, height, and pliability in all groups, with directionally greater improvement in the combination group; the superiority of the combination group did not reach statistical significance, although improvement in pliability, vascularity, and color was more pronounced in immature scars ^[12]. The 2025 RCT of 5-FU combined with ultra-pulsed fractional CO2 versus laser alone showed greater VSS and PSAS improvement and a 93.33% total effective rate in the combination arm versus the laser-alone arm ^[29]. The 2025 Er:YAG plus intralesional triamcinolone split-scar RCT showed that 52.9% of combination-arm scars achieved more than 75% reduction in thickness versus 26.5% in the laser-alone arm (P < 0.05) ^[30]. The pattern across these RCTs is that laser-assisted drug delivery and combination laser modalities outperform single-laser monotherapy on validated scar-scale endpoints.

Controversies and Evidence Gaps

Heterogeneity precludes pooled meta-analysis for ablative fractional laser

The 2021 systematic review of ablative fractional laser treatment of hypertrophic burn and traumatic scars across 23 studies found that significant heterogeneity among studies precluded meta-analysis of pooled data; the authors concluded that there is abundant existing literature on AFLs in the management of hypertrophic scar but study heterogeneity limits generalizability, with the explicit call that future studies should prioritize standardized protocols including assessments of function and quality of life ^[5]. The 2017 systematic review of laser therapy for hypertrophic burn scars across 12 studies concluded that overall quality and risk of bias issues were present in all studies and that insufficient scientific evidence exists to determine the effectiveness of laser therapy from that review, calling for randomized controlled trials with more rigorous designs ^[6]. The 2021 VSS-only meta-analysis acknowledged that the heterogeneity of treatment regimens across studies limits the ability to provide specific treatment recommendations ^[3]. The honest read is that the AFCO2 evidence base shows directional consensus on benefit while lacking the standardization needed for protocol-level recommendation.

PDL: strength of effect debated

The strength of pulsed dye laser effect on hypertrophic burn scar beyond pruritus and erythema is contested. The only randomized controlled trial of PDL with a within-patient control in burn scars is the 2003 Allison trial of 585 nm PDL across 38 patients in four age and scar-maturity groups, which showed null effect on Vancouver score, photographic assessment, and surface profile at 6 and 12 months between treatment and control sites (Vancouver P = 0.876 at 6 months and P = 0.680 at 12 months; photographic P = 0.006 at 6 months and P = 0.329 at 12 months; surface profile P = 0.552 at 0, P = 0.107 at 6, and P = 0.227 at 12 months); only pruritus improved significantly between treatment and control (P < 0.001) ^[7]. The 2011 systematic review reported low efficacy for PDL 585 nm and moderate efficacy with PDL 595 nm in hypertrophic scars, with insufficient evidence for comparing efficacy of different laser therapies ^[9]. The 2025 ELABS RCT showed patient-rated improvement at 6 months but no significant improvement in observer-rated POSAS, quality-of-life, or colour measurement, and early PDL was not cost-effective at the £20,000/QALY threshold ^[19]. The 2025 systematic review of PDL, fractional CO2, or combination for burn scar treatment showed that PDL was associated with significantly greater reduction in total VSS than combination therapy (MD -0.90), while AFCL showed no significant difference ^[11]. The signal is that PDL has the strongest evidence for pruritus and erythema and the only controlled RCT of PDL with a within-patient control showed null on objective scar-scale endpoints; PDL's role is most secure in immature, vascular scars and in symptomatic erythematous scar where pruritus and erythema are the targets.

Cost-effectiveness and access

The 2025 ELABS RCT documented that early pulsed dye laser was not cost-effective at the £20,000 per QALY willingness-to-pay threshold at 6 months follow-up, with the authors noting that longer-term follow-up is required for definitive cost-effectiveness conclusions ^[19]. Access to laser therapy is uneven; the 2025 multi-state ambulatory-surgery dataset analysis (New York and Florida State Ambulatory Surgery and Services Databases 2014-2019 compared against the 2020 Healthcare Cost and Utilization Project National Inpatient Sample) characterized 709 laser therapy recipients and showed laser-treated patients were younger, predominantly female, and non-white, and 29.5% of laser cases came from the lowest income quartile despite 37.5% of all burn admissions coming from that quartile, indicating an access gap by socioeconomic status ^[40]. Laser therapy is generally reserved for specialized centers, while topical treatments such as silicone preparations remain suitable for general practitioner or surgical practice ^[37].

Optimal protocol: fluence, density, interval, session count

Optimal protocol parameters remain incompletely defined. The 2020 randomized trial of high- versus low-density fractional CO2 found greater VSS and POSAS improvement at higher density but with greater pain and adverse events ^[25][26]. The 2011 NAFR trial found that low-density treatment was at least as effective as high-density with fewer side effects ^[23]. The 2023 systematic review of scar age, laser type, and interval found that efficacy is influenced by the time lapse after injury, the type of laser, and the interval between treatments ^[8]. Optimal interval, energy, density, and session count have not converged across the literature, and protocols vary substantially between burn centers and individual practitioners.

Standardized outcome reporting

The 2016 prospective evaluation of FCO2 in mature burn scars observed that in scar treatment studies, the patient and observer Vancouver scar scales may not be sensitive enough to detect outcome differences ^[35]. The need for validated patient-reported outcome measures, standardized objective measures (ultrasound thickness, cutometer, perfusion imaging), and longer follow-up periods is the recurring methodological call across the systematic reviews and meta-analyses ^{[5][6][9][19]}. Until outcome reporting is standardized, cross-study comparison remains limited.

Long-term durability

Most laser burn-scar trials report 6 to 12 month follow-up. Mature burn scars evolve over years, and the durability of laser-induced improvement past 12 months is not well characterized ^[19]. The ELABS authors specifically noted that scar maturation is prolonged and dynamic and that follow-up of up to two years is required to understand the eventual clinical effect ^[19]. The 2015 NAFL trial that included 6-month histological follow-up confirmed sustained scar-scale improvement and supporting histology at 6 months but did not extend further ^[33]. Longer-term controlled data are an evidence gap.

References

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