eMedicine Specialties > Dermatology > Physical Modalities Including Laser Applications

Laser Revision of Scars

Author: Keyvan Nouri, MD, Professor of Dermatology and Otolaryngology, Director of Mohs Micrographic Surgery, Dermatologic and Laser Surgery, Director of Surgical Training, Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine
Coauthor(s): Tina S Alster, MD, Clinical Professor, Department of Dermatology, Georgetown University School of Medicine; Director, Washington Institute of Dermatologic Laser Surgery; Sonal Choudhary, MD,, Clinical Research Fellow, Department of Dermatology and Cutaneous Surgery, University of Miami; Christopher J Ballard, MD, Resident, Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine; Voraphol Vejjabhinanta, MD, Postdoctoral Fellow in Mohs, Laser and Dermatologic Surgery, Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine; Clinical Instructor, Suphannahong Dermatology Institute, Thailand
Contributor Information and Disclosures

Updated: Mar 17, 2010

Introduction

Integumental injury initiates the cascade of wound-healing events. In most cases, wound healing results in restoration of skin that is smooth and normal in appearance. Despite its normal appearance, repaired skin achieves only 70-80% of its original tensile strength. This consequence of normal healing processes does not raise concern; rather, when healing deviates from its orderly pattern, scarring results. Scars are common complications of wound healing that affect millions of individuals. Although pigmentary and vascular alterations often are transient, textural changes caused by collagen disruption often are permanent.

The wound-healing process is divided into 3 major overlapping stages: inflammation, granulation tissue formation, and matrix remodeling. The initial stage is defined by a structured sequence involving inflammatory cells. This cascade is orchestrated by neutrophils. Subsequently, macrophages elaborate a variety of cytokines, which create an environment amenable to granulation tissue formation. Finally, fibroblasts migrate into the area, proliferate, and recapitulate ontogeny by depositing new collagen, first type III and later type I. Simultaneously, angiogenic factors released into the wound environment stimulate formation of new capillaries. A problem arises when this organized process is disrupted. An overzealous healing response may occur, creating a raised nodule of fibrotic tissue. Alternatively, deleted collagen is inadequately replaced and forms a pitted appearance resembling the surface of a golf ball. In either case, the scar often is a legacy of skewed wound healing.

Although scars rarely pose a health risk, patients often present with symptoms of associated pruritus or dysesthesia. The consulting physician must not overlook the patient's perception of aesthetic disfigurement because this perception may be detrimental to the patient's psyche. The physician must take into consideration certain patient variables as well as pertinent scar characteristics.

The purpose of this article is to review the strengths and limitations of current laser technology used to improve the appearance and symptomatology of hypertrophic scars, keloids, striae, atrophic scars, and acne scars.

Related eMedicine articles include Keloid and Hypertrophic Scar, Lasers, General Principles and Physics, and Scar Revision.

Laser Principles

Atomic electrons exist at varying energy levels. Most commonly, electrons are found at the lowest most stable energy state. Energy, in the form of quanta or photons, may be absorbed or lost. If a photon is absorbed at the correct wavelength, electrons become excited and the atom becomes relatively unstable. Once unstable, the electron reverts to its resting energy level by releasing a photon of energy in a process called spontaneous emission. If an excited electron is stimulated by another photon of equivalent energy, 2 photons of equal magnitude are released in parallel fashion. An external energy source serves to increase the proportion of excited electrons, which increases the probability of stimulating another photon. This energy can stimulate spontaneous emission of radiation. The term laser is an acronym for light amplification by stimulated emission of radiation, and stimulated emission of radiation is the basis of laser technology.

Laser light has certain properties that make it useful in dermatologic therapy. Monochromaticity allows for emission of a single wavelength of light determined by the medium (gas, liquid, solid) through which the light passes. Monochromaticity permits specific absorption of laser energy by distinct cutaneous targets or chromophores such as melanin, hemoglobin, or tattoo ink. A second property, coherence, occurs as light waves travel in phase with accordance to time and space. Laser light is also collimated: it is emitted in a parallel fashion through an intense, narrow beam, which allows for the creation of a small, focused spot. Collimation permits propagation without divergence or loss of intensity along the optic fiber.

Laser-tissue interactions produce 3 effects: photothermal, photochemical, and photomechanical. Photothermal effects, which are directly derived from heat production, are the primary focus of dermatologic laser surgery. The goal of laser surgery is to direct energy to specific targets while limiting damage to adjacent tissues. To achieve this goal, the concept of thermal relaxation time must be understood and applied. Thermal relaxation time is the time needed for appropriate cooling of a given light-absorbing target within skin. When heat is produced within the target at a rate faster than the thermal relaxation time, the target becomes hot compared to its surroundings. If heat is produced at a rate less than the thermal relaxation time, the target and its environment are heated accordingly. Pulse durations used by dermatologic lasers capable of selective photothermolysis follow this principle and allow for the production of desired specificity.

Laser Treatment of Scars and Striae: Background

The early 1980s brought about a revolution in dermatologic laser treatment with Anderson and Parrish's¹ publication detailing the theory of selective photothermolysis. Selective photothermolysis describes the use of specific absorptions of laser energy to achieve temperature-mediated localized injury in a target. This theory led to the invention of pulsed lasers that are target-specific and highly selective. Increased selectivity decreased the amount of thermal damage to healthy tissue, thereby decreasing scarring and other adverse effects.

The first laser used in the treatment of hypertrophic scars and keloids was a continuous-wave argon laser. While initial reports were encouraging, subsequent studies did not confirm its efficacy. Similarly, use of the continuous wave neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (1064 nm), which selectively inhibits collagen production by a direct photobiologic effect and creates tissue infarction with subsequent charring and sloughing of the treated area, also showed initial clinical improvement. Results, however, were transient and scar recurrences were common. Similar recurrences were observed when hypertrophic scars and keloids were excised or vaporized with a continuous-wave carbon dioxide laser. When treated with the carbon dioxide laser, scars universally recurred within 1 year.

By the early 1990s, the effectiveness of the vascular-specific 585-nm pulsed dye laser (PDL) in treating a variety of vascular lesions (eg, port-wine stain, telangiectasia) was widely known. The first series of studies on the successful use of the 585-nm flashlamp-pumped PDL in the treatment of hypertrophic scars and keloids had been published. In 1993, Alster and colleagues² reported prolonged improvement in argon laser–induced port-wine stain scars treated with PDL irradiation. Skin surface texture analysis performed by optical profilometry with accompanying clinical assessment revealed that laser-irradiated scars approximated normal skin characteristics. No scar recurrences were noted 4 years following treatment.

In 1994, Alster³ reported clinical and textural improvement in long-standing erythematous and hypertrophic scars. An improvement rate ranging from 57-83% was observed following 1-2 PDL treatments, respectively. Dierickx and colleagues⁴ corroborated these findings the following year; they reported an average scar improvement of 77% after 1.8 laser treatments. Not surprisingly, in 1995, Alster and Williams⁵ compared the clinical, textural, histologic, and symptomatic responses of irradiated scar halves with untreated control halves. Significant improvement was observed for all clinical parameters. Histologic evaluation revealed increased numbers of regional mast cells. Because mast cells also elaborate a variety of cytokines, the presence of mast cells following laser irradiation and accompanying tissue revascularization may provide an explanation for the therapeutic outcome following microvasculature destruction in terms of stimulating collagen remodeling.

Subsequent studies also showed improvement in keloid scars following PDL treatment. In 1996, Alster and McMeekin⁶ also reported improvement in erythematous and hypertrophic facial acne scars following 585-nm pulsed dye irradiation.

Improvement in nonerythematous, minimally hypertrophic scars was also achieved following combination treatment involving pulsed dye technology and carbon dioxide laser vaporization. In 1998, Alster and Lewis⁷ treated selected scars by performing carbon dioxide laser de-epithelialization followed by PDL irradiation. Significant and prolonged clinical and textural improvement was observed in all treatment areas. In a 1995 report, Goldman and Fitzpatrick⁸ also described a combination approach to scar management. They used intralesional corticosteroids concomitantly with 585-nm PDL irradiation in 11 of 37 patients with hypertrophic scars.

No consensus exists regarding the mechanism by which PDLs achieve these additional clinical effects. Plausible explanations include laser-induced tissue hypoxia (leading to collagenesis from decreased microvascular perfusion), collagen fiber heating with dissociation of disulfide bonds and subsequent collagen realignment, selective photothermolysis of vasculature, suppression of TGF-β₁ expression,  and mast cell factors (eg, histamine, interleukins, various immunofactors) that may affect collagen metabolism.

In 1996, McDaniel and colleagues⁹ reported using the same 585-nm PDL to effect an improvement in the appearance of striae. They observed an improvement not only in skin surface appearance, but also in increased dermal elastin after low-fluence laser irradiation. In a 1998 report, Alster and colleagues⁷ also found that low-fluence PDL irradiation was superior compared with pulsed dye treatment at regular (scar) fluences and pulsed carbon dioxide vaporization. Both groups postulate that the improvement may be due to laser-induced effects on elastin, collagen, or other undiscovered factors.

In 2003, Nouri and colleagues¹⁰ showed that the 585-nm PDL can improve the quality and appearances of surgical scars when used as early as the day of suture removal. Scars were treated 3 times at monthly intervals and were significantly more improved compared with controls in overall Vancouver Burn Scar Scale (ie, vascularity, pliability, height, and cosmetic appearance) comparisons.

Scar Characteristics

Proper scar classification is important. Subtle differences in clinical characteristics indicate the diagnosis and treatment protocol. Qualities such as color, texture, and morphology affect the fluences used and the number of predicted treatments required for revision. The physician should also consider the number and results of previous treatments.

Hypertrophic scars versus keloids

Hypertrophic scars are pink, raised, firm, erythematous scars characterized by a decreased expression of collagenase. They occur because of overzealous collagen synthesis coupled with limited collagen lysis during the remodeling phase of wound healing. The result is formation of thick hyalinized collagen bundles consisting of fibroblasts and fibrocytes. Collagen bundles are arranged in nodules. Despite obvious tissue proliferation, hypertrophic scars remain within the confines of the original integumental injury. Hypertrophic scars and their keloid counterparts usually form in body areas that exhibit slow wound healing or in pressure-dependent or movement-dependent areas. Scars usually form within the first month following injury. Approximately one third of patients report pruritus and dysesthesia. Unlike keloids, hypertrophic scars may regress over time. See the image below:

Striae distensae

Striae, or stretch marks, are linear bands of atrophic or wrinkled skin. They form because of rapid weight loss or weight gain in areas that have been excessively stretched, such as the abdomen, hips, breasts, and joints. Dermal inflammation and dilated capillaries mark the initial presentation, which results in an erythematous appearance with characteristic pink, lavender, and purple hues. Later, striae appear hypopigmented and fibrotic. Pathogenesis remains unclear, although estrogen and mast cell degranulation with elastolysis may be contributing factors. See the image below:

Atrophic scars are dermal depressions most commonly caused by collagen destruction during an inflammatory skin disease such as cystic acne or varicella. Surgery and trauma may also result in atrophic scars. On skin, these pitted lesions form a surface resembling a golf ball. Most patients attempt to camouflage lesions with makeup; however, scar appearance is often exacerbated by makeup, which enhances problematic textural variations.

Acne scars

Atrophic acne scars are the most common types. Less frequently, acne scars can be either hypertrophic or keloidal. Two major types of atrophic scars include superficial, erythematous macular scars and deeper scars resulting from a dermal process. Superficial scars typically do not require more than topical sunscreen or retinoids. However, when the scars involve the dermis, deeply occurring inflammation affects lower structures within the skin and leads to atrophy of the overlying skin.

Atrophic acne scars can be classified into 3 basic types: ice-pick, rolling, and boxcar scars. Ice-pick scars are usually narrow (<2 mm), sharply demarcated tracts that can reach deep into the dermis or even the subcutaneous tissue. They are typically wider at the epithelial surface and taper as they go deeper. The next type, rolling scars, tend to be shallower, wider (4-5 mm), and produce an undulating appearance in otherwise normal-appearing skin. This rise and fall of the skin surface is from abnormal fibrous attachment of the dermis to the subcutis. Boxcar scars are also wider than ice-pick scars, but they do not taper. These round- to oval-shaped skin dimples have sharp margins. They can be either shallow (0.1-0.5 mm) or deeper, but most tend to have diameters from 1.5-4 mm.

See the image below:

Patient Variables

When evaluating a potential candidate for laser surgery, the physician must consider certain factors that may make the candidate less than ideal. Although they are not contraindications to laser surgery, these factors are indicators to proceed with caution. Physicians should be aware that these factors may complicate both surgical and postoperative management.

Darker skin phototypes

Racial background is an important consideration when assessing the likelihood of a scar developing into a keloid or hypertrophic scar. Hypertrophic scars and keloids affect approximately 4.5-16% of blacks and Hispanics. Whites are less susceptible, with a white-to-black susceptibility ratio estimated at 1:3.5 to 1:15. Likewise, the physician must consider racial background when contemplating outcomes of laser treatment. The presence of increased epidermal pigment in darker skin tones (phototypes III or greater) interferes with the absorption of PDL energy by hemoglobin. As a result, the amount of energy effectively delivered to dermal scar tissue is reduced.

This phenomenon raises 2 concerns: (1) efficacy of laser scar treatment is reduced, and (2) destruction of epidermal melanin results in postoperative hypopigmentation. When considering cutaneous laser resurfacing with the carbon dioxide or erbium:yttrium-aluminum-garnet (Er:YAG) laser, the patient and the treating physician must be prepared for the possibility of transient post-treatment hyperpigmentation.

Concurrent inflammation or infection

Infectious and inflammatory processes must resolve before performing laser surgery. In cases of bacterial or viral infection (eg, herpes simplex, verrucae), the physician must consider that infection may koebnerize by laser irradiation. In cases of concurrent inflammatory skin disorders (eg, cystic acne, psoriasis, dermatitis), the condition may worsen with laser treatment, and dermal inflammation may impede postoperative healing and clinical effects.

Medication use

Patients with atrophic acne scars are likely to have a history of isotretinoin use. Isotretinoin can foster the development of hypertrophic scars because of its effect on collagen metabolism and wound repair. Therefore, patients must have completed their last course of isotretinoin at least 6 months prior to laser resurfacing.

Unrealistic expectations

Currently, no treatment offers 100% improvement. Patients who would not consider laser therapy successful with less than 100% improvement have unrealistic expectations and are not good candidates. Patients should realize that some degree of scarring persists and multiple re-treatments may not completely eradicate the scar(s). Additionally, patients must understand their role in proper postoperative skin care. Strict patient compliance is necessary for optimal results, and a potentially noncompliant patient is not a good candidate.

Treatment Options

Treatment of hypertrophic scars and keloids

In these cases, PDL therapy is usually performed on an outpatient basis. General or intravenous anesthesia is unnecessary because the snapping sensation caused by the laser produces minimal discomfort. If anesthesia is desired, topical lidocaine cream (eg, 30% lidocaine powder in a water-miscible cream base) with or without occlusion for 30 minutes is sufficient. The eutectic mixture of lidocaine 2.5% and prilocaine 2.5% cream or Liposomal lidocaine 4% cream with or without occlusion for 30-60 minutes prior to treatment are other viable alternatives. Completely remove all creams with wet gauze immediately prior to laser irradiation. Patients with scars in sensitive body locations (eg, lips, breast, perineum, fingers) may benefit from intralesional injections or nerve block.

Consider moistening hair-bearing areas within the treatment site with water or saline to reduce thermal conduction through singed surface hairs. Always avoid flammable substances such as alcohol or acetone. The patient and all operating room personnel must wear protective eyewear.

Surgical technique calls for a series of adjacent nonoverlapping laser pulses delivered across the entire scar breadth. Treat the entire scar at each session. The scar's size, thickness, location, and color, as well as the patient's skin type, determine energy density. Less fibrotic scars in sensitive skin areas (eg, anterior chest and breast) require lower energy densities; thicker or darker scars can be treated with slightly higher fluences (see Pulsed dye laser treatment considerations and protocol in Summary).

In general, treatments should begin at lower fluences, allowing for flexibility of upward adjustment depending on scar response. If the initial treatment session produces good results, energy density should remain constant on subsequent treatments. If minimal results were achieved, consider increasing treatment fluences by 10%. If the patient reports postoperative vesiculation or crusting, consider a lower fluence with special attention to operative technique (avoidance of overlapping pulses).

Postoperative purpura following treatment with the vascular-specific PDL usually resolves within 7-10 days. During the healing process, the patient should avoid extraneous manipulation of the treatment area. Showers are permitted, but care should be taken to pat lased areas dry. Gentle cleansing of the treatment area with water and a mild soap followed by application of a topical ointment is the daily postoperative care protocol. A nonstick bandage should cover the treatment area. Evaluate the treatment area in approximately 6-8 weeks, at which time another laser treatment can be delivered if necessary.

The most common side effect is hyperpigmentation of irradiated skin. Hyperpigmentation spontaneously fades with avoidance or protection from sun exposure. If hyperpigmentation is present, consider postponing subsequent laser treatments to avoid interference from a competing chromophore (or target), such as melanin. Consider prescribing a hydroquinone-containing cream (applied qd-bid) to speed up the fading process.

Occasionally, patients develop allergic contact dermatitis secondary to topical antibiotic use or irritant dermatitis from an adhesive bandage. If post-laser rash is present, determine if it is a normal purpuric response or nonpurpuric and unrelated to laser irradiation. If concurrent pruritus is reported, consider contact dermatitis. A mild topical corticosteroid cream should be applied until the dermatitis resolves. Immediately discontinue the offending agent.

Most hypertrophic scars have an average of at least 50-80% improvement after 2 laser treatments. Keloid scars and more fibrotic hypertrophic scars usually require additional laser treatments to achieve desired results.

Treatment of striae

The 585-nm flashlamp-pumped PDL is used in the treatment of striae, which respond best to lower energy densities (3 J/cm²). Adjacent nonoverlapping laser pulses are delivered such that each individual stria is covered. Irradiated striae do not typically exhibit the characteristic purpura observed with the treatment of hypertrophic scars and keloids. Because of lower fluences, striae usually appear mildly pink, which represents mild postoperative tissue hyperemia and edema. Vesiculation and crusting should not occur when proper fluences and operative technique are used. Typically, only 1-2 treatment sessions are necessary to obtain desired results.

Postoperative management is similar to the protocol followed by patients treated for hypertrophic and keloid scars. Instruct patients to gently cleanse treatment areas with water and a mild soap. A topical ointment should be applied daily and the treatment area covered with a nonstick bandage. Advise patients to avoid sun exposure to the treatment area during the course of treatment.

Treatment of atrophic scars

Recontouring of atrophic facial scars with carbon dioxide and Er:YAG laser vaporization has become popular in recent years. Through selective ablation of water-containing tissue, both laser systems offer predictable reproducible vaporization of tissue, yielding better control compared to dermabrasion. In a 1996 study comparing the histologic depths of ablation after laser resurfacing, dermabrasion, and chemical peels, Fitzpatrick and colleagues demonstrated that skin vaporization and residual necrosis depths secondary to carbon dioxide laser resurfacing were directly proportional to pulse energy and the number of laser passes delivered. During laser resurfacing, the epidermis and a variable portion of the dermis are destroyed, with reepithelialization occurring from adjacent pilosebaceous glands. With the use of the carbon dioxide laser in particular, the production of increased numbers of myofibroblast and matrix proteins is enhanced as a result of controlled collagen denaturation (heating).

Pulsed Er:YAG lasers are 10 times more selective for water than their carbon dioxide counterparts; therefore, they result in enhanced tissue vaporization and reduced residual thermal damage. Postoperative erythema is decreased; however, the limited photothermal effect on tissue is countered by an overall decrease in clinical improvement. Thus, short-pulsed Er:YAG laser resurfacing falls short of delivering the collagen shrinkage, or tightening effect, observed with carbon dioxide laser treatment. Overall, the Er:YAG laser is effective in resurfacing skin with mild atrophic scars, yielding similar results to that of the carbon dioxide laser. In this particular setting, the Er:YAG may be the preferred method of treatment, offering comparable clinical effects with shorter postoperative recovery times.

Regardless of the system, goals are 2-fold: (1) to soften the transition between the atrophic indentation and the intact (normal) skin surrounding it and (2) to stimulate collagen production within the atrophied area. The entire cosmetic unit must be treated to minimize textural or color mismatch. If treating an isolated scar, consider spot resurfacing. In an effort to decrease treatment time when lasing large cutaneous areas, a scanning handpiece should be used. Once de-epithelialization is achieved (typically requiring 1 pass with the carbon dioxide laser at 300 mJ and 2-3 passes with the Er:YAG laser at 5 J/cm²), the scar edges, or shoulders, can be further sculpted with additional vaporizing laser passes. Partially desiccated tissue should be removed with saline-soaked or water-soaked gauze after each laser pass to prevent charring.

Typically, 300 mJ energy and 60 watts power with variable-sized and variable-shaped patterns are the parameters used with the computer pattern generator (CPG) scanning device (Coherent UltraPulse). Scanning devices attached to other carbon dioxide laser systems (Sharplan FeatherTouch or Luxar NovaPulse) can be used at 5-20 watts per scan, depending on the system and severity of scarring. Scan sizes ranging from 4-10 mm in diameter are delivered to the treatment area. Treatment usually requires 2-3 passes, and the physician should take care to remove all partially desiccated tissue between passes. Individual scar edges can be further sculpted using smaller diameter spots or scans following treatment of the entire cosmetic unit.

The Er:YAG laser is used with a 5-mm spot size at 1-3 J (5-15 J/cm²) to de-epithelialize and sculpt individual scars. A laser technique similar to the carbon dioxide system is used with Er:YAG; however, because Er:YAG vaporization does not typically produce a significant quantity of partially desiccated tissue, wiping between laser passes is not necessary except in hair-bearing areas (to reduce thermal conduction to skin through singed surface hairs). Bleeding typically is observed by the third laser pass as the result of dermal penetration and the inability of the Er:YAG laser to photocoagulate blood vessels.

Regardless of which laser is used, treated skin appears erythematous and edematous immediately postoperatively, with further worsening for the next 48 hours. Symptomatic palliation may be achieved with application of topical ointments, semiocclusive dressings, or cooling masks. The first postoperative week is critical. Closely monitor patients for appropriate healing responses and complications such as dermatitis and infection. For Er:YAG laser resurfacing, reepithelialization typically takes 4-7 days, whereas carbon dioxide laser resurfacing requires 7-10 days.

Patients who have full-face procedures or treatment to large areas should receive appropriate prophylactic antimicrobials (eg, oral antibacterial, oral antifungal, and antiviral medications) during the reepithelialization process. Avoid use of topical antibiotics on acutely irradiated skin because of the high rate of allergic or irritant contact dermatitis. Erythema is most intense and prolonged after carbon dioxide laser resurfacing (3-4 mo average). Patients who undergo Er:YAG laser treatment have minimal erythema 1-2 weeks postoperatively.

Irradiation with either laser system may provoke a number of immediate and long-term adverse effects, especially when proper protocols have not been followed. A significant adverse effect is transient hyperpigmentation. Although hyperpigmentation is more common in patients with darker skin tones, it may occur in any skin type. Transient hyperpigmentation is observed early in the postoperative course, occurring approximately 1-2 months after treatment.

The process is self-limiting, but resolution may be hastened with bleaching creams (eg, hydroquinone, arbutin) or acid preparations (eg, glycolic, retinoic, azelaic, kojic, ascorbic). Hypopigmentation is a relatively late sequela of treatment (typically observed >6 mo postoperatively) and appears to be permanent. Fortunately, true hypopigmentation (with total loss of pigment) is rare. Rather, relative hypopigmentation is frequently observed because of obvious color differences compared with adjacent nontreated (actinically bronzed) skin.

Infection is another postoperative concern because reepithelializing skin is vulnerable to bacterial (eg, pseudomonas, staphylococci), viral (eg, herpes simplex), and fungal (eg, Candida organisms) infections. Incidence is lowered with appropriate use of prophylactic antibiotics and, more importantly, aggressive postoperative wound care. Suspected infection must be diagnosed and treated early.

The most severe complications of laser resurfacing include hypertrophic scarring and ectropion formation, which are both due, in large part, to aggressive intraoperative laser technique. Hypertrophic burn scars can be effectively treated with 585-nm PDL irradiation as described earlier; ectropion typically requires surgical reconstruction.

Cutaneous laser resurfacing of moderate atrophic scars with the carbon dioxide laser yields a mean improvement of 50-80%. Collagen remodeling with further scar improvement may occur for 12-18 months postoperatively, so consider postponing re-treatment of residual scars for at least 1 year to accurately gauge clinical improvement. The Er:YAG laser system, although effective in the treatment of atrophic scars, does not offer the same amount of collagen remodeling as does the carbon dioxide laser system. The Er:YAG laser should be reserved for sculpting of individual scar edges and treatment of mild acne scars.

Treatment of acne scars

Laser resurfacing is a recent addition to the armamentarium of options for acne scarring. Lasers are relatively safe and effective options that remodel the skin to improve its appearance. In addition to lasers, numerous modalities can be used to treat acne scars, including excision, punch grafting, subcision, cryosurgery, dermal fillers, chemical peels, and silicone sheeting compression. Ice-pick scars usually extend too deep into the dermis to be reached by conventional treatments and may require a punch modality for removal. For rolling scars, therapies should be aimed at treating the irregular underlying anchoring between the dermis and subcutis. Therefore, laser revision is usually limited to shallow boxcar and superficial scars.

Ablative laser resurfacing with either a carbon dioxide or Er:YAG laser may be beneficial. After the initial treatment, allow the skin to heal, which may take 6-8 weeks. The postoperative erythema may last for up to 12 weeks. The scars can be treated with additional laser sessions to achieve the desired dermal remodeling and skin appearance.

As stated, resurfacing with a carbon dioxide laser can carry many potential risks such as delayed post-treatment hypopigmentation and scarring as well as prolonged healing after the procedure. This ablative laser can be effective alone for scarring after acne, but the risks must be considered before a patient undergoes this procedure. To enhance the selectivity of the carbon dioxide laser, some have tried combining it with an erbium laser, which is taken up more preferentially than the carbon dioxide beam. The erbium laser's cutaneous destruction is much more localized because the energy dissipates quickly within the targeted tissues. This procedure is more selective and less damaging to the skin than the carbon dioxide laser resurfacing.

The carbon dioxide laser can be used to first treat the scar, followed by irradiation with an erbium laser to further remodel the ablated, carbon dioxide–treated tissue. This speeds the wound healing process and reduces the potential complications associated with only using a carbon dioxide laser.

In contrast to ablative resurfacing, nonablative lasers do not noticeably disrupt the skin's epidermis, but they deliver thermal energy and damage the underlying dermis. These lasers induce collagen remodeling and production, which is predominantly collagen type III. In time, the collagen expression changes to contain a greater proportion of type I collagen. With these lasers, clinical improvement usually requires more than one treatment and results can continue to improve months after the laser treatments have been completed.

Alster and McMeekin⁶ in 1996 demonstrated that the 585-nm PDL could improve erythematous and hypertrophic acne scars. In 22 patients, significant improvements in texture and redness were seen after 1 or 2 treatments (6-7 J/cm²; 7-mm spot size). Six weeks following only one laser treatment, the mean improvement was 67.5%. Eight of the patients received an additional laser treatment and saw an average improvement of 72.5% 6 weeks later.

Atrophic acne scarring has been treated with a 1064-nm Q-switched Nd:YAG laser. Eleven patients with mild-to-moderate atrophic scarring were treated with 5 laser sessions at 3-week intervals. The laser was set at an average fluence of 3.4 J/cm², 4- to 6-nanosecond pulse duration, and a 6-mm spot size. Skin roughness was significantly better (23.3%) 1 month after the fifth laser session. Further improvements continued with time. At the 6-month follow-up, patients demonstrated a statistically significant 39.2% improvement from baseline measurements. This sustained improvement is likely from an enduring dermal collagen remodeling after the laser treatments have concluded. The long-term results and safety profile (ie, mild-to-moderate erythema, pain, pinpoint petechiae) allow this laser to be a viable option for patients with mild-to-moderate atrophic acne scars.

The 1320-nm Nd:YAG laser with a built-in cryogen cooling spray has been used for acne scarring. In 2004, Sadick and Schecter¹¹ treated 8 patients with 6 monthly irradiations of 3 passes each and found a modest improvement. Ice pick scars without fibrosis responded more favorably than those with fibrous tracts. Statistically significant improvements were noted in 7 of the 8 patients 5 months and 1 year after their final treatments. When only 3 treatments were used, another study found that atrophic scars improved the most. In Asian patients, there may be only a mild response. Of 27 patients treated, 8 had no objective improvement, and 9 were only mildly better than at baseline. This modality may produce better results if combined with another modality, such as surgery or an intense-pulsed light source (IPL).

A 2004 comparison by Tanzi and Alster¹² evaluated the efficacy of a 1450-nm diode laser versus a 1320-nm Nd:YAG for atrophic facial scars. Twenty patients with mild-to-moderate scarring each received 3 monthly treatments. Each half of the patient's face was randomized to one of the two lasers. After completing the treatments, the greatest clinical effect was seen at 6 months, which was consistent with the observed histologic increase in collagen production. Only modest improvements were seen with both lasers, but the 1450-nm diode resulted in greater improvements. Both lasers are safe, noninvasive options to improve the appearance of mild-to-moderate facial atrophic scars.

A recent laser technology, the fractional lasers, deliver high-intensity light fractionated through focussed lenses to uniformly generate arrays of microscopic columns of thermal injury surrounded by uninjured tissue. Tiny columns of injury are termed microscopic thermal-treatment zones. The operator can adjust the energy of the laser and the density of the microscopic thermal-treatment zones. Many fractional laser devices have been approved for the treatment of acne scars, periorbital rhytides, skin resurfacing, soft tissue coagulation, and melasma.¹³

The undamaged surrounding tissue allows for a reservoir of viable tissue, permitting rapid epidermal repair, decreasing patient down time. Both ablative and nonablative fractional lasers have been tried successfully for the treatment of scars.

In a 2009 study, the efficacy and safety of the nonablative 1540 nm erbium:glass fractional laser in the treatment of surgical and posttraumatic scars was evaluated. A histological study was conducted on a postsurgical scar to follow the time course of healing post treatment and the impact of the fractional treatment on normalization of scar tissue, as compared with baseline histologic findings of the scar. Histologic findings demonstrated rapid reepithelialization of the epidermis within 72 hours of treatment. Remodeling of scar tissue with renewal and reorganization of collagen fibers in the dermis was noted 2 weeks post treatment. Relative to baseline, 73% of treated scars improved 50% or more and 43% improved 75% or more.¹⁴

Additionally, a new combination therapy is suggested that incorporates dot peeling (the focal application of higher trichloroacetic acid concentrations), subcision, and fractional laser irradiation. In a pilot study, the efficacy and safety of this method was investigated for the treatment of acne scars. Acne scar severity scores decreased by a mean of 55.3%. Eighty percent of the patients reported significant or marked improvement.¹⁵

Cho et al studied the efficacy and safety of single-session treatments of 1550-nm erbium-doped fractional photothermolysis systems and 10 600-nm carbon dioxide fractional laser systems for acne scars through a randomized, split-face, evaluator-blinded study with 8 patients with acne scars. Half of each subject's face was treated with a fractional photothermolysis system and the other half was treated with a carbon dioxide fractional laser system. At 3 months after the treatment, the mean grade of improvement based on clinical assessment was 2 ±0.5 for the fractional photothermolysis system and 2.5  ±0.8 for the carbon dioxide fractional laser systems.¹⁶

A 2010 pilot clinical study demonstrated that lasers could also be used immediately after surgery to reduce the appearance of scars. The LASH (Laser-Assisted Skin Healing) technique induces a temperature elevation in the skin, which modifies the wound healing process. Capon et al demonstrated that 810-nm diode laser treatment, performed immediately after surgery, can improve the appearance of a surgical scar. The dose plays a significant role in scar improvement and must be well controlled. They also suggested that LASH could be used for hypertrophic scar revision.¹⁷

Summary

Current laser technology permits successful treatment of various types of scars and striae. Properly classifying the type of scars and striae present and determining which laser system provides optimum results are imperative. The 585-nm PDL is best used to treat hypertrophic scars, keloids, and striae. The pulsed carbon dioxide and Er:YAG laser systems effectively resurface atrophic scars. Future laser technologic advances and the addition of concomitant lasers and other treatments may further enhance clinical results.

Clinical Responses of Scars to Laser Therapy

Open table in new window

Pulsed dye laser treatment considerations and protocol

• Preoperative consideration
  • Skin types I-III are best suited for treatment.
  • Hypertrophic scars are more amenable to treatment.
  • Treat all body locations when possible.
  • Patients should not take anticoagulants.
• Intraoperative considerations
  • In most circumstances, use topical anesthesia or no anesthesia.
  • Energy densities may be as follows:
    • 4.5-5.5 J/cm² (10-mm spot)
    • 6.0-7.0 J/cm² (7-mm spot)
    • 6.5-7.5 J/cm² (5-mm spot
  • Deliver adjacent, nonoverlapping spots.
• Postoperative considerations
  • Patients should use a topical antibiotic ointment.
  • Advise the patient to use sunscreen and avoid sun exposure.
  • Evaluate for re-treatment at 6-8 weeks.
  • Consider bleaching for hyperpigmentation.

Carbon dioxide or Er:YAG laser resurfacing of atrophic scars

• Preoperative considerations
  • Skin types I-II are best suited for treatment.
  • This laser is used for nonpitted atrophic scars.
  • Facial scars respond best.
  • Previously treated scars are more difficult to treat.
  • Patients should discontinue isotretinoin at least 6 months prior to treatment.
  • Patients should be free of concurrent infection and inflammatory disease.
• Intraoperative considerations
  • Intravenous anesthesia is used in most cases.
  • Use energies that exceed critical vaporization threshold (>5 J/cm²).
  • Remove partially desiccated skin between passes.
  • Dampen hair-bearing areas.
  • Avoid flammable substances.
• Postoperative considerations
  • Patients should use healing ointments and semiocclusive dressings.
  • Patients should use ice or cooling masks as needed.
  • Close follow-up is necessary.
  • Patients should frequently clean skin.
  • Consider prophylactic antibiotics and pain or sleep medications.
  • Observe for and treat adverse effects and complications as early as possible.

Related clinical trials include The Effects of Fractional Carbon Dioxide (CO2) Laser Treatment Prior to Wound Closure and Burn Scar Appearance After Treatment With Fractional Carbon Dioxide (CO2) Laser.

Multimedia

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Media file 1: Erythematous and hypertrophic laceration scars before (A) and 3 months after (B) a second 585-nm pulsed dye laser treatment. Improvement in scar redness, symptomatology (decreased pruritus), and thickness were achieved. Courtesy of Tina S. Alster, MD.

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Media file 2: Keloid scar on the anterior chest before (A) and several months after (B) a second 585-nm pulsed dye laser treatment. While decreased erythema and scar bulk are noted, further pulsed dye laser treatments are necessary (at bimonthly intervals) to provide further scar improvement. Courtesy of Tina S. Alster, MD.

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Media file 3: Erythematous (early) striae distensae before (A) and after (B) a single 585-nm pulsed dye laser treatment. Reduction in erythema and mild improvement of skin surface texture were observed. Courtesy of Tina S. Alster, MD.

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Media file 4: Atrophic acne scars before full-face carbon dioxide laser resurfacing (A). Six months after the procedure (B), mild improvement was observed in terms of scar severity and skin surface texture. One year later (C), further clinical improvement was apparent because of continued and prolonged collagen remodeling. Courtesy of Tina S. Alster, MD.

Keywords

laser revision of scars, laser scar revision, wound healing, inflammation, granulation tissue formation, matrix remodeling, photothermal effects, photochemical effects, photomechanical effects, light amplification by stimulated emission of radiation, photothermolysis, neodymium:yttrium-aluminum-garnet laser, Nd:YAG laser, carbon dioxide laser, CO2 laser, erbium:yttrium-aluminum-garnet laser, Er:YAG laser, pulsed-dye laser, PDL, ablative laser, non-ablative laser, keloids, hypertrophic scars, striae, stretch marks, hypopigmentation, hyperpigmentation, atrophic scars, acne scars, acne scarring, pitted skin, skin pits

The authors and editors of eMedicine gratefully acknowledge the contributions of previous author, Ivy J Groover, MD, to the development and writing of this article.

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