Laser Complications

Issues of Concern

Burns, scarring, dyspigmentation, ocular injury, and infection can occur with almost any type of laser therapy.[1][2][3][4][5] These complications result from selective photothermolysis that is misdirected at an unintended target or applied with disproportionate energy. When a laser acts on a chromophore, the absorbed energy heats the surrounding tissue, sometimes excessively. To reduce the risk of complications from thermal injury, many laser devices use pulse durations shorter than the target tissue's thermal relaxation time (ie, the time required for the tissue to cool to its baseline temperature). Thermal relaxation times for specific tissues may vary from several nanoseconds to several milliseconds.

When used appropriately, selective photothermolysis delivers sufficient energy to destroy the target chromophore without damaging surrounding tissue.[2][4] The most effective way to avoid injury to nontargeted tissue is to deliver laser energy as precisely as possible. This approach requires patient cooperation to remain still throughout the procedure, which may necessitate pharmacologic assistance. In addition, placing wet towels around the treatment area to protect exposed skin can help prevent inadvertent burns, particularly with ablative lasers, whose energy is absorbed primarily by water.

Due to photothermal effects of laser energy, both targeted and adjacent nontargeted tissue may be injured by overheating, particularly when the treatment area contains a high concentration of chromophore (eg, a port wine stain or dark tattoo). Burns can result from long pulse durations, excessive fluence (the energy applied to the treatment area, measured in J/cm²), and insufficient cooling. The risk of burns is higher with laser devices that deliver energy via continuous beams compared with pulsed or fractionated beams. Newer devices reduce the risk of complications by delivering pulses in the picosecond-to-nanosecond range, using multiple rapid bursts in a quasi-continuous manner, or generating extremely short, high-power pulses that allow adequate thermal relaxation.[2]

The addition of various cooling devices can also help limit the heating of nontargeted tissue. Many modern laser devices have built-in cooling systems that can be used before, during, or after treatment. Cooling techniques can be divided into 2 categories: contact and noncontact. Contact cooling approaches include the use of a refrigerated tip on the laser handpiece to actively cool the skin during treatment, as well as applying ice packs before and after the procedure. Noncontact approaches include the use of cryogen sprays and forced refrigerated air.[6] The choice of cooling technique is typically determined by the capabilities of the laser device and the clinician's preference, but its use ultimately can make an important difference in preventing complications.

Dyspigmentation

Hypopigmentation and, more commonly, hyperpigmentation are relatively frequent complications of laser treatment. The risk of dyspigmentation is highest in patients with Fitzpatrick skin types III to VI and in those with darker skin tones. This risk may be reduced by avoiding sun exposure before and after laser treatment and by using fractionated laser delivery systems, picosecond (Q-switched) pulses, and cooling devices. Fractionated delivery typically is available for ablative lasers, whereas Q-switching is more commonly associated with nonablative lasers. Excessive cooling, however, may cause inflammation and can also trigger hyperpigmentation.[7]

Hyperpigmentation may result from the accumulation of extracellular melanin following the destruction of melanocytes or from increased melanin production due to posttreatment inflammation. As a result, it typically resolves within 3 to 4 months.[8] Hyperpigmentation is typically best treated by bleaching the affected skin with topical 4% hydroquinone, which prevents melanin synthesis by blocking tyrosinase. Other treatment options include superficial chemical peels, broadband light or nonablative laser treatments, and cosmetic camouflage.[9] Avoiding sun exposure is also important; therefore, laser facial resurfacing, particularly continuous-wave ablation, is best avoided during the summer months.

Hypopigmentation is less common than hyperpigmentation, and its onset can be delayed. The pathogenesis of hypopigmentation is not fully understood, although inflammation and damage to epidermal melanocytes due to excessive fluence settings or too many treatments appear to contribute.[10][11][12] Hypopigmentation is more challenging to treat than hyperpigmentation and is less likely to resolve spontaneously. In 1988, Nanni and Alster reported that up to 10% of patients undergoing laser hair removal with alexandrite and ruby lasers experienced posttreatment hypopigmentation.[13]

Depending on the device used, patterns corresponding to the laser handpiece tip may be visible, or circular patches of hypopigmentation may develop after treatment.[11][14] Excessive overlap of treatment zones can lead to burns and dyspigmentation, whereas too much intervening spacing between spots may result in noticeable areas of untreated skin.[2] Scarring and dyspigmentation may appear weeks to months after treatment. Several approaches to managing hypopigmentation have been described, including concealment with cosmetics, controlled exposure to sunlight or ultraviolet light, blue laser therapy, topical corticosteroids, fractionated CO₂ lasers, and topical prostaglandins.[15][16][17]

Burns

Burns occur when excessive photothermal heat or insufficient cooling leads to overheating of the targeted tissue. Proper patient selection and conservative fluence settings help reduce the risk of this complication. Testing treatment parameters on a small area of skin 2 to 3 weeks before the procedure may further reduce the risk of complications by allowing the clinician to titrate energy delivery in an inconspicuous area first; this technique is often used in laser hair removal.[2][18] 

During treatment, graying of the tissue indicates excessive fluence and is most apparent during nonablative vascular treatments, particularly PDL therapy of erythematous lesions or scars. If graying occurs, the procedure should be discontinued, and the device settings and cooling systems reevaluated. The ideal clinical endpoint treatment for large vascular lesions is purpura, which generally appears quite rapidly after energy delivery.

Most laser devices have failsafe systems that prevent more energy from being delivered than the settings indicate, even in the event of a malfunction. However, a malfunctioning device may deliver less energy than expected, causing the settings to be incorrectly titrated and potentially resulting in the delivery of excessive fluence after the device is repaired. For this reason, conservative settings should be used for the initial treatments after a laser has been serviced.

When burns develop, hemorrhagic crusts and ulcerations may appear several days after treatment and may indicate additional complications, including scarring and dyspigmentation.[12] Patients treated with excessive fluence may also report unusually high levels of pain, particularly compared with prior treatments. Burn severity varies widely, ranging from prolonged erythema to tissue necrosis. Ulcerations from cutaneous burns after laser treatment may resemble infections, particularly herpesvirus reactivation.

Proper technique and conservative settings are essential for reducing the risk of burns. When using a vascular laser, clinicians should recognize that lesions with a more erythematous appearance contain higher concentrations of oxyhemoglobin and therefore absorb more laser energy than less erythematous lesions; lower energy settings are often sufficient for treatment. Similarly, lower settings are recommended when treating lesions overlying bone, such as those on the forehead or orbital rim, because laser energy may reflect off the bone and pass through the target tissue a second time.

Beyond adjusting the energy delivery settings, various cooling devices may also reduce the risk of cutaneous burns. Burns resulting from laser therapy can be treated with immediate cooling and subsequently managed with bland emollients and topical steroids to promote re-epithelialization.[11] To prevent secondary infection, deeper burns may require topical antimicrobials such as silver sulfadiazine and mafenide acetate.

Infections

Infection is one of the most common complications following laser treatments, particularly ablative resurfacing, because these procedures disrupt the skin barrier. For this reason, active infection is generally considered a contraindication to ablative resurfacing. Cutaneous infections may present atypically after ablative resurfacing and can resemble burns or delayed wound healing due to the absence of the epidermis. Clinicians should therefore maintain a low threshold for empiric treatment and for culturing these lesions to determine the definitive diagnosis.[2][12]

Reactivation of herpes simplex virus (HSV) commonly occurs following laser treatment, particularly with resurfacing of the perioral skin; therefore, antiviral prophylaxis is often recommended.[19] HSV reactivation typically presents as localized or diffuse painful erosions with or without vesicles that develop within a week after treatment. These lesions most often occur in the perioral region but may involve the entire face.

Bacterial pathogens may also cause posttreatment infections. Common organisms include Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. Bacterial infections usually present as nonhealing erosions accompanied by erythema, honey-colored crusting, or purulent exudate and may be difficult to distinguish clinically from HSV reactivation. In immunocompromised patients or in those who leave occlusive dressings in place for prolonged periods after treatment (more than 72-96 hours), superficial candidal infections may occur. These infections may present as persistent erythema or intense pruritus developing up to 2 months after treatment.[10][12][11]

Due to the comparatively high risk of HSV reactivation following perioral laser resurfacing and the high prevalence of latent HSV infection in the general population (up to 80% of adults in the United States), antiviral prophylaxis is recommended for 7 to 14 days after the procedure, even in patients with no known history of HSV infection.[20] An effective prophylactic regimen is oral valacyclovir 500 mg twice daily for 14 days, beginning the day before the laser treatment.[21] If HSV reactivation occurs despite adequate prophylaxis, intravenous antiviral therapy may be required, although this outcome is rare. Because HSV infection following laser procedures carries a risk of scarring and bacterial superinfection, it should be treated promptly and aggressively.[2][10][11][12]

Antibacterial prophylaxis for laser resurfacing is controversial. If an infection is suspected, a low threshold for culture is necessary, but routine prescription of antibiotics before laser resurfacing is uncommon. Due to the risk of scarring, antibiotic therapy should be initiated promptly if a bacterial infection is suspected. Empiric antibiotic therapy such as doxycycline or trimethoprim-sulfamethoxazole should cover S aureus, but ciprofloxacin may be required if cultures are positive for P aeruginosa or E coli.[10]

Scars

All patients should be counseled on the potential risk of scarring, especially those undergoing ablative resurfacing. Laser devices can induce scarring from burns, excessive treatment depth, abnormal wound healing, or secondary infections.[10] 

During skin resurfacing, the treatment goal is to reach the papillary dermis rather than the reticular dermis, as deeper penetration increases the risk of scarring. When the papillary dermis is exposed, the skin develops a slightly yellow appearance that resembles chamois leather. In addition, pinpoint bleeding from subdermal perforating vessels may occur, although it may take several seconds to up to 1 minute to become visible. For this reason, repeat laser passes should not be performed prematurely, as doing so may lead to underestimation of the treatment depth.

Nonablative lasers used to treat vascular and pigmented lesions, as well as laser hair removal, can burn the surrounding tissue and lead to scarring, particularly with excessive fluence. Lesions with a limited vascular supply also may be more susceptible to necrosis and subsequent scarring if laser treatment further compromises tissue perfusion; more conservative settings applied over a greater number of treatments will lower the risk. Posttreatment cutaneous infection or viral reactivation can also lead to scarring. Particular caution should be exercised during ablative procedures of the neck, as there is an increased risk of scarring compared to the face, likely due to a lower concentration of pilosebaceous units and a thinner dermis.[10]

Patients who have undergone radiation therapy also may be at increased risk of scarring after laser resurfacing due to impaired wound healing caused by damaged microvasculature. Recent isotretinoin use is not necessarily a contraindication to laser resurfacing and does not always increase the risk of posttreatment scarring. However, conventional wisdom generally recommends waiting 6 to 12 months after treatment cessation before undergoing laser resurfacing.[22][23]

Patients should be advised to follow up promptly if there is evidence of scarring following laser procedures to initiate early treatment. Scars from laser therapy are treated similarly to other types of scars using topical or intralesional steroids, silicone gel, or silicone sheeting. In many cases, laser resurfacing may be the best treatment for scarring, even if the primary cause was a laser. Some patients may develop persistent grid or checkerboard patterns on the skin following fractionated resurfacing, which may self-resolve but may also benefit from continuous-wave ablative resurfacing, particularly for patients with lighter skin types (Fitzpatrick skin types I-III).

Ocular Injury

Laser devices present a potential risk of ocular injury to patients and healthcare personnel in the treatment environment through direct beam exposure or reflected radiation, including specular (mirrorlike) and diffuse reflections. Various structures may be damaged depending on the target chromophore. Ablative (CO₂ and Er:YAG) lasers target water and can therefore damage the cornea. Nonablative (Nd:YAG, ruby, and alexandrite) lasers targeting vascular or pigmented structures act on oxyhemoglobin and melanin, which may result in retinal damage. The Nd:YAG laser is associated with the highest risk of ocular injury, particularly in light-eyed patients who lack chromophores in the iris to absorb laser energy. The long wavelength (1064 nm) of this laser allows it to pass easily through the aqueous and vitreous humors to reach the retina.[24] To prevent ocular damage, all parties in the treatment environment should wear eye protection rated for the laser wavelength being used. In some cases, it may be more practical for the patient to wear metal eye shields, particularly if periocular skin resurfacing is planned.[5]

In all cases, warning signage should be placed outside the treatment room to prevent healthcare personnel without eye protection from entering the room and risking ocular injury. Covers should also be placed on the windows to prevent laser energy from escaping the room. Ocular injuries from laser treatment can lead to permanent blindness and are considered emergencies. Permanent blindness is more likely to occur in cases of direct ocular exposure, which should prompt immediate consultation with an ophthalmologist.[25]

Symptoms of an ocular injury include a bright flash of colored light and, occasionally, a popping sound coinciding with the firing of the laser, typically followed by reduced visual acuity and possibly floaters in the visual field. Corneal injuries may be managed similarly to corneal abrasions. Superficial cases can be treated with topical antibiotics and patching or placement of a bandage contact lens, whereas more severe injury with scarring or vision loss may require corneal transplantation. Topical corticosteroids may also be prescribed; however, if the retina is involved, corticosteroids may need to be administered by injection or implantation.[26] Steroids help reduce inflammation and promote epithelial healing while preserving photoreceptor cell function.[26] Other effective medications may include topical prostaglandins, vitamin C, and vascular endothelial growth factor inhibitors; however, some cases might ultimately require surgical intervention.[27]

Rare Adverse Effects

Paradoxical hypertrichosis

Although uncommon, paradoxical hypertrichosis is a recognized adverse effect of laser hair removal. This condition is reported most frequently in patients with Fitzpatrick skin types III and IV and tends to occur on the jawline, cheeks, neck, shoulders, back, and upper arms. The exact cause of the hypertrichosis in this setting remains unknown, but it is hypothesized that subtherapeutic thermal injury to the follicular vasculature may trigger an inflammatory response, stimulating thicker hair growth.[28] To minimize the risk of paradoxical hypertrichosis, treatment should be performed with adequately high fluence settings. Management of paradoxical hypertrichosis is similar to that for other forms of unwanted hair and may include epilation, electrolysis, or additional laser hair removal with appropriately adjusted device settings.[29]

Acneiform eruptions

Postprocedural use of occlusive healing ointments and biosynthetic dressings may cause acne and milia, especially in patients prone to acne. These eruptions most often develop within the first few weeks after laser treatment, while the skin is in the re-epithelialization phase.[30] In most cases, treatment is not required, as the acne typically resolves when occlusive ointments and dressings are discontinued. However, for more severe eruptions, management may include a short course of doxycycline or tetracycline, or intralesional corticosteroid injections for individual inflamed cysts.

Koebner reactions

Recent evidence has raised the question of whether laser therapy may induce the Koebner phenomenon in susceptible patients.[31] Although uncommon, laser-induced Koebner reactions have been reported, particularly with hair removal. The proposed mechanism involves localized thermal injury to the skin and surrounding blood vessels when melanin within hair follicles is targeted, which may trigger a Koebner response in treated areas. Additionally, the number of treatment sessions appears to have a role in distinguishing true Koebner reactions from pseudo-Koebner reactions. A single session usually triggers a true Koebner reaction, as most trauma and inflammation occur during the initial treatment. In contrast, vascular lasers may show an inverse pattern, with cumulative injury developing over multiple sessions.

A retrospective study further demonstrated that patients undergoing laser hair removal experienced worsening of skin disease if active lesions were present and the treatment was directed to the disease site.[32] In patients with active skin disease, caution should be exercised, and laser treatment should be avoided in the affected areas.

Clinical Significance

Laser devices are powerful tools with an expanding array of clinical indications, but they also have the potential to cause considerable harm to patients and healthcare providers if not used appropriately. Laser procedures should be performed only by trained professionals in appropriate medical settings to ensure high-quality care and reduce the risk of adverse effects and subsequent litigation.[33]

Clinicians should be aware of the potential complications associated with laser procedures and of appropriate management strategies. Early recognition and treatment of laser-related complications can help reduce long-term morbidity and the need for additional interventions. All members of the healthcare team share responsibility for the safety of both patients and colleagues. Essential safety measures include the use of appropriate eye protection and personal protective equipment by everyone in the procedure room, as well as ensuring that water and a fire extinguisher are readily available.[2][5]

Enhancing Healthcare Team Outcomes

Laser procedures should be approached with caution, particularly because many are performed for cosmetic indications, where high patient expectations and low tolerance for adverse effects increase the potential impact of complications. Clinicians should carefully evaluate candidates for laser therapy and exercise caution when treating patients with darker skin tones, who are at increased risk of dyspigmentation and paradoxical hypertrichosis; these patients should be counseled regarding these risks. The Nd:YAG laser carries a lower risk of dyspigmentation in patients with darker skin tones but should be used only by experienced operators due to its potential for deep tissue penetration.[34]

Strict sun avoidance for approximately 2 weeks before treatment can reduce the risk of postinflammatory hyperpigmentation. Although this condition typically resolves over several months, management may include continued sun avoidance, superficial chemical peels, and topical hydroquinone. Hypopigmentation may resolve spontaneously or be concealed with makeup. Melanin production may also be stimulated through controlled exposure to sunlight, fractionated CO₂ laser therapy, or narrow-band UV light.[2][11][35][15]

Laser devices are commonly operated by physicians, physician assistants, and nurse practitioners. As laser procedures carry an inherent risk of complications, optimal patient outcomes depend on a coordinated team approach that emphasizes careful patient selection, thorough patient education, strict adherence to safety protocols, and effective communication among members of the healthcare teams.