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Management of acne scars

Management of acne scars
Literature review current through: Jan 2024.
This topic last updated: Jan 07, 2022.

INTRODUCTION — Acne vulgaris is a common skin disease that frequently results in scarring [1,2]. Scars secondary to acne can lead to physical disfigurement and the psychosocial impact can be profound [3]. Early and effective treatment of acne is the best means to minimize and prevent acne scarring. (See "Acne vulgaris: Overview of management".)

Although a variety of therapies may reduce the prominence of acne scars, no therapy removes acne scars completely. A multimodality approach to scar treatment is usually necessary to achieve the best cosmetic results. The selection of an approach to treatment is based upon factors such as the type and degree of acne scarring, patient preference, side effects, cost, and treatment availability.

The management of scarring secondary to acne vulgaris will be reviewed here. The therapeutic approach to active acne is reviewed separately. (See "Acne vulgaris: Overview of management".)

PATHOGENESIS — Acne scarring represents an altered wound healing response to cutaneous inflammation that leads to an imbalance in matrix degradation and collagen biosynthesis. Although scarring is a common consequence of inflammatory acne vulgaris, not all patients develop scarring [4]. The reasons for discrepancies in the propensity to scar are not clear.

One theory focuses on a role for the nature of the inflammatory response in determining which patients develop scarring. This concept is supported by an immunohistochemical study of 8 patients not prone to acne scarring and 11 patients prone to acne scarring [4]. Specimens from early lesions from patients who were not prone to acne scarring demonstrated a large, active, nonspecific immune response that subsided with lesion resolution. In contrast, patients prone to acne scarring had a smaller, more specific immune response in early lesions that was increased and activated in resolving lesions. This persistent inflammation in healing tissue may contribute to scarring.

CLASSIFICATION — Acne scars can be divided based upon morphology into atrophic scars and hypertrophic scars. An individual patient may have more than one type of scar:

Atrophic scars – Atrophic scars, the most common type of acne scars, are caused by destruction and loss of collagen in the dermis and present as indentations in the skin. Destructive inflammation in the deep dermis and subsequent contraction is thought to result in the indented appearance [5].

Atrophic scars may be subclassified into ice pick, rolling, and boxcar scars [6]:

Ice pick scars – Ice pick scars are usually narrow (<2 mm), deep, sharply demarcated tracts that can extend into the deep dermis or subcutaneous tissue. Ice pick scars are typically wider at the epithelial surface and taper as they go deeper [6].

Rolling scars – Rolling scars are usually wider (4 to 5 mm) and more shallow than ice pick scars and produce an undulating appearance in otherwise normal-appearing skin. The rise and fall of the skin surface is due to abnormal fibrous attachment of the dermis to the subcutis [6].

Boxcar scars – Boxcar scars are wider at the base than ice pick scars and do not taper. These round- to oval-shaped skin dimples have sharp margins and can be either shallow (<0.5 mm) or deep (>0.5 mm) [6,7].

Hypertrophic scars and keloids – Hypertrophic acne scars and keloids are less common than atrophic acne scars and are characterized by collagen gain subsequent to the resolution of an acne lesion, resulting in a firm, raised papule or plaque. Hypertrophic scars do not extend beyond the margin of the original wound [8,9]. In contrast, keloids extend beyond the margin of the original wound. (See "Keloids and hypertrophic scars".)

The clinical appearance of both atrophic and hypertrophic acne scars may be accentuated by erythema. The treatment of erythema in acne scars is an important (and often initial) component of treatment. (See 'Treatment of erythema' below.)

Patients often use the term acne scars to refer to the persistent postinflammatory hyperpigmentation (picture 1) that is a common side effect of acne, particularly in individuals with dark skin (skin phototype IV to VI (table 1)). Unlike the permanent textural changes that result from true scarring, pigmentary changes tend to slowly improve over time. (See "Acne vulgaris: Overview of management", section on 'Postinflammatory hyperpigmentation'.)

PRETREATMENT ASSESSMENT — The pretreatment clinical assessment is an essential component of acne scar treatment. The pretreatment assessment serves to determine whether the patient is a good candidate for treatment and allows the clinician to obtain a clear understanding of the patient's expectations and tolerance for certain procedures.

Patient interview — We begin our evaluation by eliciting the specific concerns and expectations of the patient and the patient's medical history. This discussion helps the clinician to identify treatments that will best address the patient's concerns and helps the clinician to begin to assess risk for side effects of treatment. We review the following:

Patient's specific concerns about scar appearance and desired outcome of treatment

Status of acne (resolution of acne is preferred prior to acne scar treatment) (see 'Precautions' below)

History of acne treatment including isotretinoin use (recent isotretinoin use may impact wound healing) (see 'Precautions' below)

History of poor wound healing, keloid formation, or postinflammatory hyperpigmentation

History of other skin disorders (particularly disorders that may appear or worsen at sites of skin injury, such as lichen planus or psoriasis) and medical disorders or medications that may affect risk for infection or poor healing

Prior cosmetic procedures in the site of treatment

In addition to the points above, a discussion with the patient to obtain a clear understanding for the patient's ability and willingness to tolerate side effects is of critical importance for developing an appropriate plan for treatment. While some patients may be willing to tolerate the discomfort, risks, and long recovery period associated with an aggressive and often very effective procedure, such as traditional ablative laser resurfacing, other patients may be willing to accept lesser benefit in exchange for less aggressive treatment.

Physical examination — The physical examination allows the clinician to assess the characteristics of acne scars to determine the treatment approaches that are likely to be beneficial. Direct overhead lighting will accentuate the scars, facilitating the visualization of scars and scar features [10]. Key features to identify on the physical examination of acne scars include:

Type of scars (ice pick, rolling, boxcar, hypertrophic, or keloidal; scar type influences the response to specific treatments) (see 'Classification' above and 'Focal treatment of scars' below and 'Individual atrophic acne scars' below)

Color of scars (the appearance of erythematous acne scars can be improved with vascular laser treatment) (see 'Treatment of erythema' below)

Depth of scars (superficial procedures may have little effect on deep scars)

Location of scars (nonfacial scars are more resistant to therapy than facial scars, [10] and nonfacial skin has a lesser capacity for regeneration after resurfacing procedures [11])

The physical examination should also include an assessment for features that may increase the risk for poor outcomes from certain treatments. Key features to recognize include:

Scar distensibility do scars disappear when surrounding skin is gently stretched? (Scars that are not distensible, including ice pick scars and tethered scars, will not respond well to injectable soft tissue fillers)

Palpable fibrosis beneath scars (if present, scar excision or a procedure to remove or release the tethering fibrosis [eg, excision or subcision] is necessary prior to other treatments)

Keloidal or hypertrophic scars in other body areas (suggests increased risk for scarring)

Skin color (patients with dark skin color [skin phototypes IV to VI (table 1)] have elevated risk for postinflammatory hyperpigmentation as a consequence of certain treatments [eg, some resurfacing procedures and chemical peels] [12]) (see 'Precautions' below)

Review of treatment expectations and risks — An in-depth discussion with the patient about expected treatment outcomes and side effects is essential prior to proceeding with treatment. A clinician who does not have a clear understanding of the patient's desired outcome and tolerance for side effects may select a treatment regimen that is overly or insufficiently aggressive. In addition, poor communication between the clinician and patient about the expected degree of improvement from a procedure may result in a dissatisfied patient despite an outcome that the clinician perceives as excellent for a particular procedure.

In general, patients receiving treatment of acne scars should be informed that:

Acne scars are rarely completely or almost completely removed

Several procedures may be required to obtain optimal correction

A recovery period may be required depending on the treatment(s) selected (eg, traditional ablative resurfacing may require a recovery period of up to two weeks)

The side effects of each procedure being considered should be discussed in detail with the patient. Infection, hyperpigmentation, prolonged erythema, swelling, poor wound healing, and scarring are risks associated with many acne scar procedures. Because acne scar therapy is an elective procedure, knowledge of expected side effects and risks strongly influences the willingness of patients to undergo specific procedures. Patients who are educated about the characteristics, risk, and expected outcomes are empowered to make informed decisions regarding treatment. Financial considerations also may limit the ability of patients to proceed with certain treatments.

Precautions — Certain patient characteristics increase risk for adverse effects from acne scar treatment. Examples of very common characteristics that impact treatment risk include:

Active acne – Patients with active acne should first have the disease under control with topical or oral treatment, as indicated, before beginning treatment for acne scarring. There is no point in treating acne scars if acne is not under control because new scars will continue to form after scar treatment.

Recent isotretinoin therapy – Patients seeking laser resurfacing for acne scars often have a history of severe acne and may have received isotretinoin therapy. There has been concern regarding increased risk for impaired wound healing and excessive scarring following cutaneous procedures performed within 6 to 12 months after isotretinoin therapy. However, a systematic review found insufficient evidence to support delaying manual dermabrasion, superficial chemical peels, cutaneous surgery, and ablative or nonablative fractional laser procedures secondary to recent isotretinoin therapy [13]. Delaying traditional ablative laser resurfacing procedures is still recommended [13].

Skin phototype IV to type VI (table 1) Patients with dark skin tones are at increased risk for procedure-related postinflammatory hyperpigmentation. Diffuse, widespread hyperpigmentation lasting one year or more can follow ablative laser resurfacing and is a common side effect of medium and deep chemical peels [14]. Procedures with less risk for hyperpigmentation, such as fractional laser resurfacing, skin needling, injectable soft tissue fillers, and subcision are preferable for patients who desire less risk for this side effect.

TREATMENT — Overall, high-quality trials of interventions for acne scars are lacking. A systematic review of randomized trials found insufficient evidence to recommend any particular intervention as first-line treatment [15]. More high-quality placebo-controlled trials are needed to clarify the efficacy of treatments. The approach to treatment reviewed here is based upon a review of the available evidence and consideration of the practical aspects of treatment.

The ideal treatment regimen for acne scars is efficacious for the types of acne scars present and reflects the level of patient tolerance for transient side effects. In the clinical setting, clinicians must work with patients to identify a treatment regimen that is consistent with the relative importance of these factors for the patient. A patient who is very uncomfortable with treatment risk may prefer a regimen that may be less effective because it is low risk.

Generalized atrophic facial acne scars — Frequently, patients who present for the treatment of facial acne scars have multiple scars, a presentation that is best managed with a field approach to treatment. Patients who require treatment of only a few specific scars can be managed with some of the same treatments. (See 'Individual atrophic acne scars' below.)

Because no single treatment completely removes acne scars, a multimodality approach to generalized facial acne scars is most likely to provide the best results from treatment. Our ideal result-focused approach to generalized atrophic facial acne scars can be summarized in three key steps:

Step 1 – An initial treatment phase that consists of the treatment of erythema within scars (if present) and focal treatments to target individual scars that are likely to be resistant to collagen remodeling procedures

Step 2 – A collagen remodeling procedure (the gold standard is full-face resurfacing with a traditional ablative laser)

Step 3 Additional treatments designed to address resistant scars and augment the results of the collagen remodeling procedure (eg, injectable soft tissue fillers, additional nonablative or ablative fractional laser treatments)

However, this result-focused regimen usually is not feasible because it requires high patient tolerance for invasive and time-consuming procedures and long recovery periods. Therefore, we usually sculpt a regimen from this framework that maximizes results within the boundaries of the patient's tolerance for side effects. The therapeutic options for each step are reviewed below.

Step 1: Treatment of erythema and challenging scars — The goal of the initial treatment phase is the treatment of scar erythema and individual scars that are likely to be resistant to collagen remodeling procedures.

Treatment of erythema — The treatment of scar erythema is an important component of acne scar treatment because erythema accentuates acne scars and makes scars more noticeable to the observer. Treatment of erythema can improve the appearance of acne scars even without improvement in the more difficult to correct textural abnormalities. Pulsed-dye laser (PDL) therapy is the treatment of choice for scar erythema.

Pulsed-dye laser — Pulsed-dye laser therapy improves erythema in scars by targeting oxyhemoglobin within vascular structures in the skin. (See "Laser and light therapy for cutaneous vascular lesions", section on 'Principles of laser therapy'.)

Efficacy of this treatment for acne scars is supported by a split-face, observer-blinded study in which 22 patients with erythematous and/or hypertrophic facial acne scars had one cheek treated with one or two treatment sessions with a 585 nm flashlamp-pumped dye laser (0.45 ms pulse, average fluence 6.5 J/cm2, 7 mm spot size) [16]. Six weeks after an initial treatment, the mean reduction in clinical erythema/scarring compared with the appearance of surrounding normal skin was 68 percent for treated areas. In contrast, significant clinical improvement was not observed in the scars on the untreated areas.

Successful treatment of acne scar erythema with a pulsed-dye laser usually requires three to four or more treatments given at approximately one-month intervals.

Other therapies — In our experience, other light-based devices used to treat vascular lesions such as the potassium titanyl phosphate (KTP) laser and intense pulsed-light devices can be effective for scar erythema. In addition, marked clinical improvement in postinflammatory erythema in acne scars has been reported after nonablative fractional laser treatment [17].

Focal treatment of scars — Deep ice pick scars and deep boxcar scars may respond poorly to laser resurfacing and other collagen remodeling procedures. Treatment of prominent scars of these types with one of the modalities below may improve the final results of treatment:

Chemical reconstruction of skin scars technique (CROSS technique):

Indication – Ice pick and narrow boxcar scars [18].

Description – A high-strength trichloroacetic acid (TCA) peel solution (100%) is placed directly in the base of scars to ablate the epithelial wall and to promote dermal remodeling.

Subcision:

Indication – Rolling acne scars; the technique is not very effective for ice pick or boxcar scars [7,19,20].

Description – A needle is inserted under the acne scar and is manipulated to release the fibrous tissue that tethers the scar and contributes to the depressed appearance [21]. An uncontrolled study of 18 patients with atrophic (primarily rolling) acne scars suggests that subcision performed with a blunt blade also may be effective [20].

When subcision is successful, new collagen forms beneath the scar without recreating a depression. Multiple treatments may be necessary to achieve significant improvement in an acne scar. Complications include swelling, bruising, bleeding, and infection [19].

Punch excision and punch elevation:

Indication – Ice pick and boxcar scars [7].

Description – Punch excision is an effective treatment for ice pick scars and small (<3 mm) boxcar scars [6]. A punch biopsy instrument of equal to or slightly greater diameter than the scar is used to incise the tissue to the subcutaneous fat layer and excise the scar. The wound site is sutured. Scar spreading and suture track marks are problems that can follow punch excisions. For scars larger than 3.5 mm, elliptical excision may be more favorable than punch excision [10].

A punch grafting procedure in which tissue from another site is placed in the site of the excised acne scar has also been used, but there may be a mismatch of tissue color and texture [6]. Results from punch excision are often better.

Punch elevation is best performed on scars with sharp edges and normal appearing bases [6]. Therefore, the procedure is best suited for boxcar scars. A punch biopsy tool that is exactly the size of the inner surface of the scar is used to incise the scar to the depth of the subcutaneous tissue. Rather than removing the tissue as is done in punch excision, the tissue is elevated and sutured at a position that is slightly higher than the surrounding skin. Contraction during wound healing leads to uniform elevation of the scar surface and surrounding skin.

Clinical experience suggests that placing a single buried suture using 6-0 Vicryl suture for punch holes that are >2.5 mm in diameter may help with wound healing and minimize spreading [6]. To minimize suture track marks, it is important that the epidermal sutures are not tightened excessively and are removed from facial sites no more than seven days after the procedure.

Step 2: Collagen remodeling procedure — Atrophic acne scars result from a loss of collagen in the dermis. Our second phase of treatment for generalized facial atrophic acne scars consists of a procedure to induce collagen remodeling. Examples of procedures that can achieve this endpoint include traditional ablative laser resurfacing, nonablative fractional laser resurfacing, ablative fractional laser resurfacing, chemical peels, dermabrasion, and skin needling.

First-line treatment — Traditional ablative laser resurfacing is the most effective method to achieve this endpoint, but is an aggressive procedure that is not tolerated by all patients. Patients typically do not need more than one treatment, but the treatment has a significant recovery period. Nonablative fractional laser resurfacing, a less aggressive and less risky procedure, is our preferred alternative to traditional ablative laser resurfacing. Disadvantages of nonablative fractional laser therapy include lesser efficacy and the requirement for multiple treatments.

Traditional ablative laser resurfacing — Traditional ablative laser resurfacing involves the use of a 2940 nm erbium:yttrium aluminum garnet (Er:YAG) laser or 10,600 nm carbon dioxide (CO2) laser. These lasers target water in the skin, resulting in the ablation of the epidermis and dermis in very precise increments. The thermal injury caused by the laser promotes collagen contraction, collagen remodeling, and skin tightening, effects that can result in improvement in the appearance of scars (picture 2A-C). (See "Ablative laser resurfacing for skin rejuvenation", section on 'Traditional ablative lasers'.)

The Er:YAG laser induces less thermal injury than the CO2 laser, a feature that translates to lesser efficacy after one treatment, shorter recovery times, and less intraoperative pain if an equal number of laser passes are administered:

Efficacy The efficacy of ablative CO2 laser resurfacing for atrophic acne scars was demonstrated in an 18-month prospective uncontrolled study of 60 patients (skin phototype I to V (table 1)) with moderate to severe atrophic facial acne scars. All patients achieved significant immediate and prolonged improvement in skin tone, texture, and appearance of treated scars [22]. One month after treatment, clinical improvement scores were improved by a mean of 69 percent. After 18 months, the mean improvement was 75 percent. Continued collagenesis and dermal remodeling were evident in histologic specimens up to 18 months after surgery.

Multiple uncontrolled studies support the efficacy of ablative Er:YAG lasers for the treatment of atrophic acne scars [23-28]. As an example, a nonrandomized prospective study that compared the efficacy of short-pulsed, variable-pulsed, and dual-mode Er:YAG lasers in 158 patients with facial acne scars found that treatment with all three lasers was associated with good to excellent improvement in ice pick and shallow boxcar scars [25]. Deep boxcar scars did not respond well to short-pulsed Er:YAG laser treatment.

Administration – Traditional ablative laser resurfacing is an intense procedure with a relatively long post-treatment recovery period (up to two weeks after CO2 laser resurfacing). Therefore, candidates for this treatment must be carefully selected. The treatment plan includes important preoperative (eg, antiviral prophylaxis), intraoperative, and postoperative measures to promote the best outcome of treatment. General preoperative, intraoperative, and postoperative measures for ablative laser resurfacing are reviewed separately. (See "Ablative laser resurfacing for skin rejuvenation", section on 'Administration'.)

Expert training is required to perform ablative laser resurfacing. The target endpoint that determines the number of laser passes during each treatment session (initial visualization of the sebaceous glands in the dermis) can be difficult to appreciate. In addition, this portion of the procedure can become disorienting secondary to bleeding. To mediate this, we laser the most dependent region first during each laser pass and proceed superiorly.

Each laser pass leaves a layer of eschar. We leave the eschar in place after the last laser pass, rather than wiping it away. This allows the eschar to act as a biologic dressing until it gently sloughs over the subsequent three to five days. Clinicians vary on preferred post-treatment wound care. Our post-treatment care consists of daily to twice daily soaks with acetic acid (1:10 dilution with water) followed by application of petrolatum; saline or water soaks are also commonly used. We do not use an overlying dressing. Patients can usually return to work approximately two weeks after CO2 laser resurfacing; the convalescent period for Er:YAG laser resurfacing is usually three to eight days.

Potential adverse effects of ablative laser resurfacing include persistent erythema, hypopigmentation (an expected effect), hyperpigmentation, infection, and scarring. Erythema is common and usually resolves within several weeks, but occasionally persists for longer. In young patients, dyspigmentation often improves over the course of 3 to 12 months. The risk for dyspigmentation is greatest in patients with skin phototypes III to VI (table 1) [29]. Because of the potential for dyspigmentation in this population, a conservative number of laser passes is prudent.

Improvement from full-face ablative laser resurfacing and the potential loss of pigmentation continue for months postoperatively. Therefore, a waiting period of 6 to 12 months is necessary prior to retreatment [22].

Nonablative fractional laser resurfacing — Nonablative fractional resurfacing (NAFR) is a frequently used alternative to traditional ablative laser resurfacing because of the lesser recovery time required after this procedure (typically one to three days [30]). Most commonly, the 1550 nm or 1540 nm NAFR lasers are used. Rather than ablating a continuous area of skin, fractional lasers emit narrow microscopic columns of laser light, which allows for the treatment of a fraction of the area of skin in the treatment area while leaving intervening areas of unaffected skin (figure 1). This translates into reduced side effects and shorter recovery times compared with traditional ablative lasers [31]. (See "Nonablative skin resurfacing for skin rejuvenation", section on 'Fractional lasers'.)

However, multiple treatments with a nonablative fractional laser are typically required to achieve satisfactory effects on scarring. Compared with traditional ablative lasers, the efficacy of nonablative lasers on dermal collagen remodelling is more limited [32]:

Efficacy – Benefit from NAFR has been reported in randomized trials; however, most of these trials have compared NAFR to other modalities rather than to placebo or no treatment [15,33]. The first randomized controlled trial to evaluate the efficacy of nonablative fractional laser resurfacing on atrophic acne scars was a split-face trial that compared the efficacy of three treatment sessions with a 1540 nm erbium-glass fractional laser at four-week intervals on one side of the face in 10 patients with no treatment on the contralateral side [32]. The response to treatment was assessed by a single blinded evaluator after 4 and 12 weeks. Statistically significant reductions in acne scar severity scores were seen on the laser-treated side but not on the untreated side. Of the 10 patients, 5 reported that the appearance of acne scars was moderately or significantly improved after treatment, 3 noted slight improvement, and 2 reported no improvement after treatment. Uncontrolled studies also suggest a beneficial effect of nonablative fractional laser treatment [34-36].

In comparison to ablative fractional laser resurfacing, available data suggest that patients treated with nonablative fractional laser resurfacing will experience a shorter duration of post-treatment erythema, a lower likelihood of postinflammatory hyperpigmentation, and less pain during the procedure, with minimal loss in the efficacy of treatment [30,31]. More trials that directly compare nonablative and ablative fractional laser therapy for acne scars are necessary to confirm this conclusion. We find that most of our patients prefer nonablative fractional laser treatment because of the expected shorter recovery time after treatment. (See 'Ablative fractional laser resurfacing' below.)

Administration – Our typical nonablative fractional laser resurfacing treatment regimen consists of four to six treatments given at one-month intervals. Treatment is usually well tolerated, but is not immune to adverse effects. In a retrospective study of 961 patients (skin phototype I to V (table 1)) treated with a 1550 nm erbium-doped fractional laser, acneiform eruptions and herpes simplex virus eruption were among the most common adverse effects, each occurring in approximately 2 percent of patients. Less common side effects included erosions, postinflammatory hyperpigmentation, prolonged erythema (>4 days), prolonged edema (>2 days), dermatitis, impetigo, and purpura. As with other resurfacing procedures, patients with darkly pigmented skin have increased risk for post-treatment hyperpigmentation.

Other collagen remodeling procedures — Traditional ablative laser resurfacing and nonablative fractional laser therapies are our preferred collagen remodeling procedures because they are precise and controlled methods of treatment [11]. However, factors such as treatment availability, clinician expertise, patient-specific risk factors, patient preference, and cost may support other therapeutic approaches. Additional treatment options include ablative fractional laser therapy, chemical peels, dermabrasion, and skin needling. An advantage of skin needling is the minimal risk for the postinflammatory hyperpigmentation that is a potential side effect of other collagen remodeling treatments.

Ablative fractional laser resurfacing — Although ablative fractional lasers (Er:YAG, yttrium-scandium-gallium-garnet [Er:YSGG], and CO2 lasers) can improve acne scars, we favor nonablative fractional laser resurfacing when it is available because available evidence suggests that ablative fractional laser treatment is associated with greater side effects and little extra benefit in the response to treatment [30,31]:

Efficacy – Multiple prospective and retrospective studies support the efficacy of ablative fractional lasers on acne scars [37-42]. This includes a single-blind intra-individual trial in which 13 patients with atrophic acne scars received three ablative fractional CO2 laser treatments at one-month intervals on one 9 to 30 cm2 scarred area on the face and no treatment on a scarred facial area of similar size and appearance. At one, three, and six months after treatment, significantly lower scores for scar texture and atrophy were present in treated areas [38].

Ablative fractional lasers may be useful for treating focal areas of hypertrophic and tethered scarring [43].

Administration – Although improvement in acne scarring can be noted after a single ablative fractional laser resurfacing treatment, multiple treatments yield the best results [37]. High fluence settings also may yield better results, but the use of high fluence settings is tempered by the potential for increased side effects. A typical ablative fractional laser treatment course consists of 6 to 10 treatments given at one to two month intervals using relatively high densities, low energy, and multiple passes. Caution is necessary, as excessive density settings may increase risk for hypertrophic scarring [44].

Treatment causes some pain, and a topical anesthetic is usually applied prior to treatment. Common side effects after ablative fractional laser treatment include erythema, edema, crusting, and scaling, all of which usually resolve within two weeks. Dyspigmentation, scarring, herpes simplex virus reactivation, petechiae, bleeding, and itching are additional potential side effects. Patients with darkly pigmented skin have the highest risk for post-treatment postinflammatory hyperpigmentation. In a randomized trial that compared two treatment regimens with a 1550 nm Er:YAG fractional laser for the treatment of facial acne scars in patients with skin phototypes IV, V, and VI (table 1), moderate postinflammatory hyperpigmentation occurred in 6 of the 15 treated patients [45]. To minimize risk for postinflammatory hyperpigmentation, treatment of patients with dark skin requires conservative energy and density settings.

Early studies suggest that autologous platelet-rich plasma may reduce recovery time after ablative fractional laser resurfacing for acne scars [46,47].

Chemical peels — Chemical peels can be effective treatments for acne scars [14,48]. As with laser resurfacing, injury to the skin caused by chemical peels can stimulate a wound healing response with collagen remodeling [49].

Chemical peels are classified into superficial, medium-depth, and deep chemical peels according to the depth of skin injury:

Superficial chemical peels, such as salicylic acid, glycolic acid, lactic acid, Jessner solution, and 10% to 25% trichloroacetic acid affect only the epidermis.

Medium depth chemical peels, such as combination treatment with Jessner solution and 35% to 50% trichloroacetic acid, injure the skin to the level of the papillary dermis.

A deep chemical peel with phenol injures skin to the level of the mid-reticular dermis.

Because of limited depth of penetration, superficial chemical peels may improve the appearance of only very superficial acne scars [50,51] and are more useful for the treatment of postinflammatory hyperpigmentation. Medium-depth and deep chemical peels are typically required to achieve more than minimal improvement in the appearance of scars.

An example of a study supporting efficacy of chemical peeling for acne scars is an uncontrolled study that reviewed the effects up to three treatments with a Jessner solution and 35% trichloroacetic acid peel in 47 patients with atrophic acne scars and light brown to dark brown skin [14]. Of the 15 patients who returned for at least one follow-up visit, all but one demonstrated clinical improvement. One patient had >75 percent clearance of lesions, eight had moderate improvement (51 to 75 percent clearance), four had mild improvement (26 to 50 percent clearance), and one had minimal improvement (1 to 25 percent clearance). Postinflammatory hyperpigmentation followed in nine patients, but resolved within three months. Healing time after this type of chemical peel is usually between 7 and 10 days.

Risk for side effects of chemical peels increase with the depth of the peel. In addition to postinflammatory hyperpigmentation, potential side effects of chemical peels include infection and scarring. Phenol chemical peels are associated with the additional risk of excessive systemic absorption resulting in cardiac toxicity [52].

Some authors propose that combining superficial chemical peels with other interventions may successfully treat acne scars without the longer recovery times and greater risk associated with deep chemical peels [48,53]. In a small single-blind randomized trial, effects of combination therapy with a 20% trichloroacetic acid peel and skin needling on atrophic acne scars were similar to the effects of a deep phenol peel [48]. (See 'Skin needling' below.)

Dermabrasion — Although acne scars were previously one of the most common indications for dermabrasion [54], the use of dermabrasion for acne scars has fallen significantly since the rise in use of laser resurfacing therapy. However, in skilled hands, dermabrasion can be highly effective for severe acne scarring.

Dermabrasion involves the use of tools (eg, high-speed brush, diamond cylinder, fraise, or silicon carbide sandpaper) to remove the epidermis or epidermis and part of the dermis [7]. An advantage of the procedure is that it allows the clinician to etch scar edges precisely without thermal injury. However, dermabrasion is highly operator dependent, requires meticulous intraoperative assistance, and has the potential for severe postoperative scarring, dyspigmentation, and milia formation.

Based upon reports of severe scarring in patients treated with dermabrasion during isotretinoin therapy, a waiting period of 6 to 12 months after completion of isotretinoin treatment is usually recommended prior to performing a dermabrasion procedure. However, successful treatment with dermabrasion within shorter periods has been documented [55].

Microdermabrasion is a more superficial procedure in which abrasive crystals (eg, aluminum oxide crystals) are propelled onto the skin within a controlled vacuum suction system. The depth of abrasion during microdermabrasion remains in the epidermis. Thus, improvement in acne scars after microdermabrasion is minimal.

Skin needling — Skin needling procedures can improve acne scars [56]. Similar to fractional lasers, needling procedures induce small columns of damage in the epidermis and dermis, leaving intervening skin untouched. A needling device typically consists of a cylinder that is circumferentially studded with 1 to 2.5 mm long needles. The device is rolled over the surface of the skin to form numerous perforations in the epidermis and dermis with a goal of stimulating neocollagenesis. Advantages of skin needling include low cost, a relatively short recovery period (two to three days) and a very low risk for postinflammatory hyperpigmentation [10,57,58].

The efficacy of needling for atrophic acne scars was evaluated in a split-face trial in which patients with facial acne scars were randomly assigned to treatment with a needling device on one side of the face and no treatment on the contralateral side [59]. The needling regimen consisted of three treatments separated by two weeks, each preceded by the application of a topical anesthetic. Only the assessors of treatment response were blinded to treatment. Analysis of 15 patients who received treatment revealed a significant decline in the scar score on the treated areas but not in the control areas six months after treatment. The mean improvement in overall scar appearance on the treated side was 41 percent. Treatment was well tolerated by patients and pain was minimal. Additional studies are needed to determine the optimal regimen for skin needling and to compare the efficacy of the procedure with other acne scar treatments.

Mild transient erythema and edema is expected after skin needling. Scarring at sites of needle entry in the skin has developed in one patient after the procedure [60].

Other — Fractional bipolar radiofrequency devices deliver energy in a matrix array that results in heating of a select portion of the epidermis and dermis. New evidence suggests that these devices can improve acne scars [61,62]. In a split-face randomized trial that compared the efficacy of a fractional bipolar radiofrequency treatment with the efficacy of skin resurfacing with a nonablative 1550 nm erbium-doped glass fractional laser, the two treatments exhibited similar efficacy [62].

The findings of an open, prospective study of 20 patients with facial acne scarring suggest that treatment with a 755 nm picosecond pulse duration laser with a diffractive lens array may be effective [63]. The diffractive lens array affects a greater surface area and has a greater pattern density per pulse. Three months after completing six treatments, the average level of improvement in the appearance of acne scars in clinical photographs was between 25 and 50 percent [63].

Assessing the response to treatment — Improvement in atrophic acne scars after collagen remodeling procedures is sometimes subtle or slow, which can make it difficult for clinicians and patients to recognize treatment benefit. High-definition photography is a useful method to follow the response to treatment.

Step 3: Adjunctive therapies — After performance of a collagen remodeling procedure, the patient is followed to assess for the response and to determine whether additional treatments would be beneficial for augmenting the response to treatment. Because collagen remodeling is a slow process, we wait at least six months prior to performing additional treatments. An exception is the treatment of persistent erythema after laser resurfacing, which we often treat with a vascular laser if present three months after the resurfacing procedure.

For patients who have undergone traditional ablative laser resurfacing and are willing to receive additional treatment, we often administer a series of four nonablative fractional laser treatments at four to eight week intervals beginning six months after ablative laser resurfacing in an attempt to augment the response to treatment. If there are resistant scars, we often replace one of the nonablative fractional laser treatment sessions with an ablative fractional laser treatment (picture 3A-B). (See 'Nonablative fractional laser resurfacing' above and 'Ablative fractional laser resurfacing' above.)

In some cases, direct treatment of specific areas of residual scarring can be greatly beneficial. Injectable soft tissue fillers are commonly used and effective treatment options for select acne scars that do not respond adequately to collagen remodeling procedures. (See "Injectable soft tissue fillers: Temporary agents" and "Injectable soft tissue fillers: Permanent agents".)

Injectable soft tissue fillers — Injection of an atrophic scar with a soft tissue filler can result in instantaneous and dramatic improvement in the appearance of the scar. The optimal scars for soft tissue filler treatment are broad, rolling scars that are soft and distensible [10], meaning they disappear when the surrounding skin is stretched. Ice pick scars, tethered scars, and scars with an atrophic center and hypertrophic border are unlikely to respond well to soft tissue filler injection. Injection of the filler beneath these scars may make the scar more prominent or result in an unnatural appearance.

High-quality trials evaluating the efficacy of soft tissue fillers for the treatment of acne scars are limited. A systematic review of randomized trials found moderate-quality evidence to support this intervention but also identified a paucity of long-term studies [15].

A wide variety of soft tissue fillers are available with varying properties. The duration of effect, clinician familiarity and experience with products, and location of scar influence choice of filler. Temporary soft tissue fillers, fillers that slowly degrade within tissue over time, are most commonly used for acne scars. With temporary fillers retreatment is usually necessary. Liquid injectable silicone, an example of a permanent filler, is a cost-effective treatment that yields long-term results, but should only be used by experienced and expert clinicians (picture 4A-B) [64,65]. Improper use of liquid injectable silicone has resulted in serious adverse effects [66-68]. Strict adherence to safety measures is critical. (See "Injectable soft tissue fillers: Temporary agents" and "Injectable soft tissue fillers: Permanent agents".)

Injection of autologous fibroblasts may be a future alternative to manufactured soft tissue fillers [69].

Individual atrophic acne scars — Patients with isolated acne scars or who are only concerned about specific scars may not require extensive collagen remodeling procedures to achieve the desired level of improvement. Procedures such as subcision, punch excision, punch elevation, chemical reconstruction of acne scars (CROSS technique), injection of soft tissue fillers, and focal dermabrasion can effectively treat individual lesions. (See 'Focal treatment of scars' above and 'Injectable soft tissue fillers' above.)

Focal treatments that are most appropriate based upon scar type are:

Ice pick scars – Punch excision or CROSS technique

Boxcar scars – CROSS for small scars, punch or elliptical excision, punch elevation, or focal dermabrasion

Rolling scars – Subcision or injectable soft tissue fillers

Nonfacial atrophic acne scars — Atrophic acne scars are most commonly found on the face, but may also occur in other areas prone to acne vulgaris, such as the shoulders, back, and chest. Studies to determine the best approach to the treatment of nonfacial atrophic acne scars are lacking.

Nonfacial atrophic acne scars and facial atrophic acne scars are similar in appearance; however, the treatment of nonfacial scars warrants additional considerations. Although many of the same therapies can be attempted, nonfacial scars are more resistant to treatment [10] and the results of collagen remodeling procedures are often unsatisfying.

Moreover, the lower density of skin appendages in nonfacial skin compared with facial skin results in lesser capacity for skin regeneration after skin resurfacing procedures, a feature that may increase risk for postprocedure scarring [11,44]. Because of this risk, treatment with traditional ablative lasers is usually avoided and conservative laser settings (eg, lower density and lower energy levels) are used for treatments with ablative fractional lasers. Care must also be taken to avoid excessive use of topical anesthesia.

Hypertrophic acne scars and keloids — Hypertrophic scars and keloids are less common than atrophic acne scars and are characterized by firm, raised lesions. The management of hypertrophic scars and keloids secondary to acne is similar to the management of hypertrophic and keloidal scars from other etiologies. (See "Keloids and hypertrophic scars".)

First-line therapy — Intralesional corticosteroid injections are the first-line therapy for keloids and hypertrophic scars [70]. The proposed mechanisms of action include decreased fibroblast proliferation and collagen synthesis along with a reduction in inflammatory mediators. Triamcinolone acetonide (10 to 20 mg/mL) is injected directly into the scar to reduce its size and thickness. Higher concentrations (up to 40 mg/mL) are used for very thick scars.

We typically repeat treatments every four to six weeks, and discontinue treatment if at least a partial response is not evident within four treatments. Dose-dependent adverse effects of intralesional corticosteroid therapy include hypopigmentation, dermal atrophy, and telangiectasias. (See "Intralesional corticosteroid injection", section on 'Adverse effects and pitfalls'.)

Additional therapies — Additional common therapies for hypertrophic scars and keloidal scars are pulsed-dye laser therapy and silicone gel sheeting (see "Keloids and hypertrophic scars" and "Laser therapy for hypertrophic scars and keloids"):

Pulsed-dye laser – Pulsed-dye laser therapy can improve hypertrophic scars and keloids. The technique requires a series of adjacent nonoverlapping laser pulses delivered across the entire scar breadth. The scar's size, thickness, location, and color, as well as the patient's skin type, determine the fluence that should be used. After an initial treatment, the fluence is maintained, increased, or decreased based upon response and side effects. Thick or dark scars usually require higher fluences than thin and light scars.

The most common adverse effect of pulsed-dye laser treatment is postoperative purpura, which often persists for several days. Pulse durations shorter than 6 ms are almost certain to cause bruising. Edema of treated skin may also occur but usually subsides within 48 hours. Treated areas should be gently cleansed daily with water and mild soap. Strict sun avoidance and photoprotection should be advocated between treatment sessions in order to reduce the risk of pigment alteration. (See "Laser therapy for hypertrophic scars and keloids".)

Silicone gel sheeting – Application of silicone gel sheeting to hypertrophic scars and keloids can result in clinical improvement. The mechanism through which benefit occurs is not fully understood. One theory is that a combination of pressure and hydration from the occlusive dressing may be responsible rather than the silicone itself. Hydration inhibits fibroblast production of collagen [71]. Other proposed mechanisms include prevention of bacteria-induced collagen production and modulation of expression of the profibrotic cytokines fibroblast growth factor-beta and transforming growth factor-beta [72]. Additionally, silicone gel sheeting may reduce pruritus, hyperpigmentation, and discomfort [73,74].

Silicone sheets are cut to the size of the scar and are worn for 12 hours per day for approximately two months. They may be applied as soon as skin re-epithelialization occurs. Adverse effects are rare and include pruritus and skin maceration.

Other – Examples of less commonly employed therapies that may be useful for hypertrophic scars and keloids include surgical excision, cryotherapy, radiotherapy, and intralesional 5-fluorouracil. (See "Keloids and hypertrophic scars".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Acne vulgaris".)

SUMMARY AND RECOMMENDATIONS

Scarring is a common consequence of acne vulgaris. Acne scars can lead to physical disfigurement and significant emotional distress. (See 'Introduction' above.)

Acne scars may be atrophic, hypertrophic, or keloidal. Atrophic acne scars constitute the most common presentation of acne scars. Atrophic acne scars can be divided into ice pick, rolling, and boxcar scars based upon morphology. (See 'Classification' above.)

A thorough pre-treatment assessment is critical prior to acne scar treatment. In addition to a medical history and physical examination, a thorough discussion with the patient is essential to ensure that the treating clinician and patient have similar treatment expectations and treatment goals. Patient tolerance for treatment side effects and recovery time strongly influences the selection of treatment. (See 'Pretreatment assessment' above.)

There is a wide variety of treatment options for atrophic acne scars, including therapies designed to remove or release fibrotic tissue, therapies to induce collagen remodeling, and therapies to fill defects. In patients with generalized atrophic facial acne scars, the best results are usually obtained through a multi-faceted approach to treatment. (See 'Generalized atrophic facial acne scars' above.)

Our first step for the treatment of generalized atrophic facial acne scars consists of the treatment of scar erythema, which can often accentuate acne scars, and focal therapies to improve deep ice pick scars, deep boxcar scars, and other scars that are likely to be resistant to other treatments. (See 'Step 1: Treatment of erythema and challenging scars' above.)

Our second step for the treatment of generalized atrophic facial acne scars is a procedure designed to induce collagen remodeling in the dermis. Traditional ablative laser resurfacing is a highly effective collagen remodeling procedure (picture 2A-C). For patients who are willing to tolerate the risks, side effects, and recovery time associated with traditional ablative laser resurfacing, we suggest treatment with this therapy (Grade 2B). (See 'Step 2: Collagen remodeling procedure' above.)

For patients who cannot tolerate traditional ablative laser resurfacing, nonablative fractional laser resurfacing is our preferred procedure. Medium-depth or deep chemical peels, dermabrasion, and skin-needling are additional examples of collagen remodeling procedures. (See 'Step 2: Collagen remodeling procedure' above.)

Patients may benefit from additional treatments following a collagen-remodeling procedure, such as additional laser treatments or injectable soft tissue fillers. (See 'Step 3: Adjunctive therapies' above.)

Patients who desire treatment of isolated atrophic acne scars may benefit from a variety of focal procedures. The morphology of the scar dictates the appropriate procedure. (See 'Individual atrophic acne scars' above.)

The management of hypertrophic or keloidal acne scars differs from the management of atrophic acne scars. For these lesions, intralesional corticosteroid injection is the first-line treatment. (See 'Hypertrophic acne scars and keloids' above.)

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References

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