image of silk fabric and dry skin

Tiffany Kwok, MD and Jaggi Rao, MD, FRCPC

Division of Dermatology and Cutaneous Sciences, University of Alberta, Edmonton, AB, Canada


Acne scarring is often challenging to manage. Various laser treatments are helpful in addressing abnormal color and texture in order to improve the appearance of an acne scar. This paper will review the appropriate use and side-effects of these laser treatments.

Key Words:
acne vulgaris, laser therapy, scarring


Scarring caused by inflammatory acne is extremely bothersome to the patient and often challenging to treat. The senior author uses a classification method for acne scarring based on both color and texture (Table 1).1 Both features must be addressed independently in order to improve the visible quality of the scar. Topical, physical, surgical, and light modalities may be used alone or in combination to improve the appearance of acne scars. This paper specifically addresses laser modalities to treat abnormalities in color and texture in acne scarring.

Scar DefectScar Type/Characteristic
  • Skin-colored/normal
  • Red
  • Brown
  • White
  • Normal texture
  • Elevated
    • Hypertrophic
    • Keloid
  • Depressed/atrophic
    • Icepick
    • Boxcar
    • Rolled
Table 1. Acne scarring classification1

Laser Options Targeting Skin Color

Red Scars

Erythema is the result of visible dilated capillaries beneath the skin surface. The intensity of the erythema is dependent on the concentration, lumen size, and depth of blood vessels. Lasers and light sources used to decrease erythema of acne scars include the pulsed dye laser (PDL), potassium-titanyl-phosphate (KTP) laser, intense pulsed light (IPL), and neodymium:yttrium-aluminumgarnet (Nd:YAG) laser. Suggested laser settings are shown in Table 2. The number of treatments will vary according to several factors including patient response after each laser session, laser technology used, and parameters of treatment.

PDL is the gold standard for treating erythema from acne scarring.2 This laser has an output wavelength of 585 nm or 595 nm, targeting oxyhemoglobin within red blood cells by approximating a major hemoglobin absorption peak at 577 nm. Treatments may be safely performed on all skin types and over hair-bearing areas without fear of follicular destruction. Tolerability of laser treatments is improved with dynamic cooling in the form of cryogen spray. Purpura occurs with extravasated red blood cells, indicating immediate vascular photocoagulation. It is advocated as a clinical endpoint of treatment, lasting a maximum of 7-10 days and resolving without sequelae.

The KTP, or frequency-doubled Nd:YAG laser, has an output wavelength of 532 nm, targeting the first peak of the oxyhemoglobin absorption curve. The penetrative depth of the KTP laser is confined to the papillary dermis of the skin and unsuitable for deeper vessels. KTP lasers generally cause only mild purpura and minimal postinflammatory hyperpigmentation on all skin types.

IPL systems are comprised of noncoherent light (approximately 500-1200 nm) released by a flashlamp within the device, which is then filtered to narrower ranges of wavelengths that simulate the monochromatic nature of true laser light. IPL devices have the benefit of larger spot sizes and a wider range of pulse duration and fluences, thereby allowing for treatment at greater depth and faster speed, coverage of larger surface areas, and concurrent therapy of multiple conditions. However, specificity for treating a single condition may be poor due to absorption competition from multiple tissue targets. Postinflammatory hyperpigmentation in darker skin types may be seen with IPL therapy.3

Nd:YAG lasers may be useful for treating erythema in scars with dilated blood vessels in the deep dermis. New microsecondpulsed Nd:YAG lasers are of benefit for targeting superficial dermal vessels due to the short pulse duration, low fluence, and quick repeated laser bursts.

LaserWavelengthPulse DurationFluenceSpot Size
Pulsed dye585 nm
595 nm
< 3 ms> 6 J/cm27-10 mm
KTP (frequency-doubled Nd:YAG)532 nm20-30 ms6-9 J/cm24-5 mm
IPLMultiple wavelengths:
approximately 500-1200 nm
common filters 560-650 nm
2.4-4.0 ms15-30 J/cm2Varies according to system used
Nd:YAG (microsecond pulsed)1064 nm0.3 ms14 J/cm25 mm
Table 2. Laser treatments for red scars

Brown Scars

Hyperpigmentation of acne scars is common, particularly with darker skin types. Lasers used to treat scar hyperpigmentation include IPL, quality-switched (Q-switched), microsecond-pulsed Nd:YAG, both confluent and fractionated ablative erbium:YAG (Er:YAG), and yttrium-scandium-gallium-garnet (YSGG). Suggested laser settings are presented in Table 3. Concomitant use of lightening creams and sunscreen, as well as sun avoidance, is advocated to further reduce scar contrast with surrounding skin.

IPL devices, with their ability to vary output wavelength, pulse duration, and fluence, can treat several skin conditions including superficial pigmentation.3 Care must be taken to protect the epidermis from overheating, which may cause pigment incontinence and further hyperpigmentation. Parallel cooling (extracting heat from the epidermis during the light pulse) is usually provided through the use of a sapphire window handpiece that generates surface cooling to approximately 5°C.

Q-switched lasers have the unique property of extremely short pulse durations, thereby allowing these devices to target very small pigment cells and particles, such as melanocytes, with minimal competition from the hemoglobin absorption curve. The Q-switched lasers, i.e., ruby (694 nm), alexandrite (755 nm), and Nd:YAG (1064 nm), are useful for treating skin pigmentation.4 The endpoint of treatment is mild superficial crusting. Care must be taken to use the lowest energy settings possible to achieve pigment reduction, as too much energy may result in punctate bleeding, cell rupture, scarring, and increased pigmentation.

Microsecond-pulsed Nd:YAG lasers (1064 nm) target both melanin pigment and small blood vessels to reduce erythema and stimulate collagen production without inducing injury to surrounding tissue. This laser may be used for any skin type.5

Confluent laser treatment involves laser light striking the entire surface of the skin in a given area, whereas fractionated laser therapy creates microscopic thermal wounds while sparing adjacent tissue over the targeted site.6 Confluent ablative Er:YAG (2940 nm) and YSGG (2790 nm) lasers have tremendous water absorption capacity, translating into vaporization of surface tissue with minimal collateral heating, limited damage to surrounding tissue, and reduced risk for further hyperpigmentation.7 These lasers ablate approximately 30 microns of the epidermis, inducing exfoliation and improving superficial hyperpigmentation. Test spots should be performed when using any ablative laser on darker skin.

Fractionated ablative Er:YAG and YSGG lasers release light energy at high peak power to create channels in skin tissue.6 These channels are physically ablated, leaving true air channels that allow removal of surrounding pigment via transepidermal elimination.

LaserWavelengthPulse DurationFluenceSpot Size
IPL> 640 nm4.0 – 6.0 ms10-25 J/cm2Varies according to system used
Q-switchedRuby: 694 nm
Alexandrite: 755 nm
Nd:YAG: 1064 nm
nanoseconds1-6 J/cm23-6 mm
Nd:YAG (microsecond-pulsed)1064 nm0.3 ms14 J/cm25 mm
Er:AYG (confluent and fractionated)2940 nmVaries according to system usedVaries according to system usedVaries according to system used
YSGG2790 nmVaries according to system usedVaries according to system usedVaries according to system used
Table 3. Laser options for brown scars

White Scars

Ultraviolet (UV) light stimulates melanogenesis in areas where melanocytes are intact. UV light can stimulate the migration of melanin-producing cells to melanocyte-deficient areas, increasing pigment in these regions.1 Excimer (excited dimer) lasers have a wavelength in the UV range (308 nm), providing concentrated melanin stimulation to white scars.

Fractionated ablative lasers (Er:YAG, YSGG, and carbon dioxide) create air channels that ultimately contract to reduce the surface area of the white scars, making them appear smaller in diameter.7

Laser Options Targeting Skin Texture

Hypertrophic Scars

When evaluating a scar that exhibits both color and elevation defects, it is preferrable to treat the texture before addressing the color, because both vascular-targeting and pigment-targeting lasers provide optimal penetration through scars that are flat and soft.1 Topical corticosteroids, alone or in combination with intralesional corticosteroids, used concomitantly with laser therapy are recommended to achieve softening and flattening of elevated scars.

Fractionated ablative lasers (Er:YAG, YSGG, and carbon dioxide) can help soften elevated scars by ablating channels of condensed collagen that contribute to the scar’s thickness and firmness.7 Fractionated ablative and nonablative lasers must be used with caution in softening elevated scars because their collateral thermal damage has the profibrotic potential to further thicken and harden scar tissue. As an aside, fractionated ablative laser treatment may also improve topical drug delivery by providing a theoretical route for transepidermal drug penetration via ablative channels created by the laser.8

Confluent ablative laser treatment (Er:YAG, YSGG, and carbon dioxide) has been shown to decrease the size and thickness of scar recurrence after surgical excision, provided laser therapy is performed at the base of the excised area immediately after surgical removal.9 Repeated pulses to the base of the excised tissue establish hemostasis and thin eschar formation. A viscous moisturizer (e.g., petrolatum) under occlusion should be applied for 3 days post-treatment, followed by a nonviscous moisturizer until the skin re-epithelializes. At the first sign of recurrent scar formation, topical corticosteroids or imiquimod are suggested to prevent progression of fibrosis.

Atrophic Scars

Depressed (Icepick and Boxcar) Scars

In treating icepick and boxcar scars, the goals are to soften the edges between the indentation and surrounding normal skin, and stimulate collagen production within the depressed area.

Resurfacing of depressed facial scars with confluent ablative Er:YAG, YSGG, and carbon dioxide lasers causes thermal injury to the epidermis and a portion of the dermis, resulting in vaporization, collagen injury, and re-epithelialization. In particular, Er:YAG lasers are highly selective for water, therefore leading to maximal tissue vaporization and reduced residual thermal damage. These devices decrease post-treatment erythema, are safe for use on darker skin types, and preferred for superficial atrophic scars due to shorter recovery times. The production of increased dermal fibrotic elements through greater collateral thermal heating capacity is enhanced with use of the YSGG and carbon dioxide lasers, making them more beneficial for deeper scars. Ablation typically requires 1 pass with the carbon dioxide laser at 300 mJ, 1-2 passes with the YSGG laser at 3.5 J/cm2, and 2-3 passes with the Er:YAG laser at 5 J/cm2. Deep treatment with the Er:YAG laser typically results in bleeding due to its limited effects on blood vessel photocoagulation.

Confluent nonablative laser treatment such as PDL, IPL, microsecond-pulsed, and Q-switched Nd:YAG lasers, as well as a variety of lasers operating in the near infrared spectrum (e.g., 1320 nm, 1440 nm, 1450 nm, 1540 nm, and 1550 nm) target water within the deeper aspects of the dermis more efficiently, thereby creating bulk heating and more collagen stimulation, referred to as subsurfacing.10 Subsurfacing may be painful, often requiring systemic analgesia.

Fractionated ablative laser treatment creates microscopic channels of thermal injury on the skin, causing skin tightening and smoothening through ablation and re-epithelialization, as well as elevation of the floor of depressed scars through collagen remodelling.11 Ablative fractional resurfacing is gentler on the skin compared with confluent resurfacing and can be safer for darker skin types; however, test spots should be performed before attempting laser resurfacing on this subset of patients. Er:YAG laser treatment is preferred for small diameter icepick and boxcar scars and for larger diameter defects in darker skin types; fractionated YSGG and fractionated carbon dioxide lasers are favored for icepick and boxcar scarring in white-skinned individuals.1

Nonablative fractional resurfacing lasers produce wavelengths in the mid-infrared range and include fractionated 1440 nm, 1450 nm, 1540 nm, and 1550 nm lasers. Nonablative lasers create zones of microthermal skin injury, requiring minimal downtime. However, the treatment process may be painful to the point of requiring oral analgesia.

Depressed (Rolled) Scars
With rolled acne scarring, treatment success depends on the degree to which the skin is bound down at the base of the scar. If the skin contour is tightly tethered, it is advisable to perform surgical subcision before other treatments to loosen the surface adhesion and dampen the tethering effect.12 Care should be taken to wait at least 2 weeks post-filler placement before attempting fractionated ablative or nonablative laser resurfacing to avoid disruption of filler placement.

Both confluent and fractionated nonablative laser treatments and fractionated ablative laser therapy may be used for rolled scars. In all cases, it is important for the laser energy to reach deeper components of the skin in order to stimulate collagen remodelling and weaken tethering adhesions.


Lasers are an important treatment option in the management of acne scarring as they can target both color and textural abnormalities. It is essential to understand both the pathophysiology of these skin defects as well as the distinct mechanisms and clinical effects of each laser. Such an appreciation enables selection of the most appropriate device and technique in order to optimize outcomes for a given patient.


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