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Alopecia: A review of laser and light therapies

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Alopecia: A review of laser and light therapies
Sophia Rangwala AB, Rashid M Rashid MD PhD
Dermatology Online Journal 18 (2): 3

Department of Dermatology, MD Anderson Cancer Center, University of Texas, Houston, Houston, Texas


Since the 1980s, laser technology has become increasingly popular to treat a variety of cutaneous conditions. Its successful use as an epilator comes with the rare but interesting side effect of paradoxical hypertrichosis. In this review, we summarize cases describing hair growth after photoepilation, as well as studies testing laser and light sources as treatment for alopecia, particularly androgenetic alopecia and alopecia areata. We also discuss the possible biologic mechanisms by which phototherapy induces hair regeneration.

1. Introduction

Initially used to treat benign vascular tumors, laser therapy is now considered first-line for removal of pigmented lesions, tattoos, scars, wrinkles, and unwanted hair. The ability of lasers to induce hair growth was incidentally noted in 1967 when Mester and colleagues used low-level laser therapy (LLLT) to treat cancer in mice with shaved backs [1]. Since then, a number of studies have suggested the use of lasers as an effective way to treat alopecia, particularly androgenetic alopecia and alopecia areata, but there is still a paucity of independent, peer-reviewed blinded clinical trials. In this review, we discuss reports of paradoxical hair growth after laser treatment, studies that utilize lasers to treat different types of alopecia, and finally, mechanisms of photo-biomodulation that may explain these clinical findings.

2. Paradoxical hair growth after laser therapy

Since approval by the Food and Drug Administration (FDA) in 1996, lasers and intense pulsed light (IPL) sources have become a popular way to terminate growth of unwanted hair because of the relative safety and efficacy of these treatments [2]. Photoepilation uses wavelengths in the red and infrared range (600-1100 nm) and is believed to work by delivering pulsed light energy to melanin in hair shafts. After absorption, the light converts to thermal energy, destroying the progenitor cells of the hair follicle while sparing surrounding tissue [3]. The biologic mechanism, however, is likely more complex than just selective photothermolysis.

Hypertrichosis is a rare but significant side effect that usually occurs after several months within and/or proximal to areas treated with laser devices [4] (Table 1). First described in 2002 with IPL therapy [5], this phenomenon has now been widely acknowledged and also referred to as paradoxical hypertrichosis, terminalization, induction, or terminal hair growth [4] The incidence rate ranges from 0.6 percent to 10 percent and appears to occur with low fluences and all laser types [4], such as diode lasers [6, 7], neodymium:yttrium-aluminum-garnet (YAG) lasers [6, 8], IPL [8, 9, 10], and alexandrite lasers [6, 8, 9, 11]. This side effect most often occurs on the face and neck, and in patients with darker skin types (III-IV), dark coarse hair, and/or co-existing hormonal imbalances [4, 8]. Interestingly, pili bigeminy has been reported in 4 cases following alexandrite or ruby laser treatment for hair removal [12, 13] and is thought to be the result of suboptimal fluences that are too low to induce thermolysis, but high enough to stimulate follicular growth [8]. Although the face and neck area appear to be most susceptible to hair induction effects, the relative sensitivity of the scalp to these effects is not known because patients do not usually seek laser hair removal for this area.

3. Androgenetic alopecia

Androgenetic alopecia, also known as male or female pattern hair loss, is a hereditary condition in which disruption of proper androgen signaling results in decreased proliferation of follicle epithelia and progressive miniaturization of terminal hairs on the scalp [14]. A recent study found that in these patients, follicular stem cell populations were preserved but downstream progenitor cell populations were significantly reduced, thus suggesting a defect in conversion from a stem cell to progenitor cell phenotype [15]. Currently, the only FDA-approved medications are finasteride and minoxidil. Because androgenetic alopecia is so common, many treatment modalities are marketed, such as topical products, supplements, and hair transplantation, but few have led to satisfactory results.

LLLT has recently increased in popularity as a stand-alone or adjunctive treatment, and is available in a home, salon, or clinical setting. The cost of available devices ranges from hundreds to thousands of dollars and the recommended course of treatment is 6 to 12 months [16]. Companies marketing these products advertise them as both thickening and inducing growth of existing follicles. In 2007, the HairMax Laser Comb® received 510(k) clearance from the FDA for the treatment of androgenetic alopecia in men [17]. This clearance means that the HairMax Laser Comb is considered a moderate-risk medical device by the FDA and is thereby solely screened for safety, not efficacy. The FDA approves a device for both safety and efficacy when it is regarded as high-risk. The HairMax Laser Comb has only been tested once in a company-sponsored study of 110 male patients, which claimed a significant increase in mean terminal hair density when compared to a sham device [18].

A consensus written by hair loss experts states that based on anecdotal experience, LLLT, particularly 650 to 900 nm wavelengths at 5 mW, may be an effective treatment option for patients. This group also found that even if no regrowth was appreciated, patients noted improvement in the texture and quality of hair [16]. Avram and Rogers conducted the first independent blinded study of LLLT and hair growth. The study had 7 patients and found that on average, there was a decrease in the number of vellus hairs, an increase in the number of terminal hairs, and an increase in shaft diameter. However, this data was found not to be statistically significant. Of note, this study used a laser “hood” and the authors acknowledge that there may have been insufficient light delivery to the scalp using this system [19].

4. Alopecia areata

Alopecia areata is the most common cause of hair loss after androgenetic alopecia. This form of hair loss usually presents as round non-scarring patches, but may have a more diffuse or complete distribution. The pathophysiology of this autoimmune disease is unknown, but recent evidence suggests it involves both innate and adaptive immune components that may be triggered by an upregulation of ULBP ligands, which in turn activate NKG2D receptors on natural killer cells [20]. Hair regrowth recurs once the inflammatory response is suppressed and the undamaged stem cells are able to regenerate the hair follicle [21]. Intralesional corticosteroids are the first-line treatment for adults and have been used for about 50 years. Despite the emergence of other topical and systemic immunomodulatory therapies in the past decade, little progress has been made for refractory cases. These treatments can also have significant side effects and a high rate of relapse [22]. Oral and topical psoralen plus UVA (PUVA) radiation has been considered in the past and although response rates have ranged from 15 percent to 70 percent in uncontrolled settings, there was no improvement over the spontaneous remission rate in large retrospective studies. In addition, high relapse rates and an increased risk of non-melanoma skin cancer have made it an unattractive option [23, 24, 25]. Photodynamic therapy has also been found to be ineffective [26, 27].

Recent case reports and clinical trials have demonstrated the 308 nm excimer laser as an effective and safe alternative for patients resistant to conventional therapies (Table 2). This laser system delivers high doses of long-wave monochromatic UVB radiation. A left-right controlled pilot study first explored the possibility of using narrowband UVB therapy via a non-laser source, but the data was not statistically conclusive because of a small sample size [28]. The first report employing a laser was in 2004 [29]. It described two patients with alopecia areata of the scalp who experienced thick and homogenous regrowth after a 9- to 11-week period of approximately weekly xenon chloride excimer laser therapy. Since this case series, only 4 additional small studies of adults and children have been published. In these reports, the excimer laser appears to produce better results for alopecia areata partialis of the scalp, as compared to alopecia areata partialis of the beard and extremities, alopecia totalis, and alopecia universalis [30, 31, 32]. With this laser, 60 percent to 77 percent of refractory patients had a complete response. Most studies compared the experimented area with a control area, with the control showing no appreciable hair growth in any study [30, 31, 32, 33]. All the published studies also indicate good tolerability by the patient, with the most common side effects being mild to moderate erythema or hyperpigmentation of the treated area. Atopic diathesis, generally a poor prognostic indicator for alopecia areata patients, was also negatively correlated with the efficacy of the excimer laser. A 308 nm excimer non-laser device showed promising results in one study, with 4 out of 8 patients demonstrating complete hair growth after a mean of 3 weekly treatments [34].

Other laser and light techniques have been effective against recalcitrant alopecia areata patches (Table 1), but need confirmation by additional studies. The Super Lizer, a Japanese linear polarized infrared light system traditionally used to treat arthralgias and neuralgias, was shown to expedite hair growth by 1.6 months for about 50 percent of patients with mild disease [35]. Another group found that a pulsed 604 nm infrared diode laser was able to induce hair growth in 94 percent of patches otherwise resistant to conventional treatments, whereas control patches remained unchanged [36]. Ninety percent of the responsive patches demonstrated terminal hair growth, whereas the remaining 10 percent had vellus hair growth.

Ho Yoo and colleagues found that weekly treatment with fractional photothermolysis induced complete hair growth after 6 months in a patient with patchy alopecia of the scalp [37]. No relapse was appreciated during the 6-month follow-up period. Fractional laser therapy is a recently introduced laser system that produces columns of “microthermal treatment zones” that extend down to the reticular dermis [38]. Because the emitted energy is absorbed mostly by water, the stratum corneum is not thermally damaged and thereby has a better side effect profile relative to other lasers.

Whereas the results mentioned above are encouraging, randomized controlled trials are needed to assess and compare these laser devices and to establish optimal therapeutic parameters. Also, combination therapies with the various other treatment modalities for alopecia areata should be tested.

5. Biologic mechanisms

The biologic events by which laser and light sources produce hair growth is unclear, but several theories have been proposed.

Hypertrichosis is the result of follicles converting from telogen (the resting phase) to anagen (the active phase), or vellus follicles transforming into terminal follicles. Sunlight has been recognized as a promoter of hypertrichosis. Although the pathogenesis is unknown, evidence shows UV radiation may upregulate production of prostaglandin E2 [39, 40], an inflammatory mediator that is known to induce reversible eyelid hypertrichosis [41] and to stimulate hair growth when applied topically on animal models [42].

When performing photoepilation, thermal energy at low fluences may not be sufficient to epilate the hair, but can still cause a perifollicular inflammatory response that persists for up to 2 weeks [4, 7]. The role of inflammation in hair induction is supported by the finding that using a cold pack after laser hair removal procedures markedly reduces the rate of hypertrichosis [8]. Local hypertrichosis has also been appreciated with other stimuli that induce local inflammation [43], such as heavy friction [44, 45, 46], burns [47], surgical incision [48, 49], and vaccinations [50, 51, 52], as well as underlying fractures [53-58], thrombophlebitis, and chronic osteomyelitis [59]. There have also been two cases in which hair induction occurred in a port wine stain and a tattoo treated with an IPL source [60].

On a cellular level, inflammation may result in increased local blood flow and release of inflammatory factors that promote follicular vascularization [4]. In normal skin tissue, the anagen phase is accompanied by follicular angiogenesis and upregulation of vascular endothelial growth factor (VEGF) in outer root sheath keratinocytes. This vasculature rapidly regresses during catagen phase. Thus, enhanced vasculature induced by inflammation may promote the development of healthy follicles. Additionally, the heat shock associated with low levels of thermal energy may upregulate heat shock proteins such as HSP-27, which have a role in follicular stem cell growth and differentiation [6].

The wound healing associated with thermal injury may also contribute to hair growth. Ito and colleagues showed that in wounds of genetically normal adult mice, de novo hair follicles form from epidermal stem cells outside the follicle [61]. Other mediators of wound healing linked to hair growth include polypeptide thymosin beta-4 [62] and cyclopentyladenosine [63]. The ability of laser treatment to induce regenerative healing has been seen in skin and many other tissues [64, 65].

In the case of alopecia areata, laser radiation may work by decreasing inflammation.

Although this is not a traditional idea, similar hypotheses exist for medicines otherwise not considered as immune modulators, particularly statins [66]. Light energy may promote T-cell apoptosis as well as induce perifollicular lymphocytes to “scatter” [29, 37]. In fact, UV-mediated immunosuppression has been well studied [67], with several studies demonstrating that exposure can inhibit contact hypersensitivity reactions [68, 69, 70] and delayed-type hypersensitivity [71, 72, 73]. Cis-urocanic acid, a chromophore and a mediator of UV-induced immune suppression, is maximally produced when skin is exposed to 280-310 nm UVB light [74]. Moreover, an immunosuppressive action spectrum for UV light, which measured suppression of nickel contact dermatitis in sensitive individuals, peaked at 300 nm [75]. These peaks correlate with the operative wavelength of the 308 nm excimer laser and thus may provide a mechanistic rationale for this laser in alopecia areata patients.

Apart from immunomodulation, direct light stimulation may activate dormant follicles, or synchronize follicles into anagen phase so that the hair density appears to be thicker [5]. Finally, follicle regeneration may be induced from a dispersal or suppression of inhibitory cells that prevent progression of follicle stem cells to progenitor cells in a manner analogous to the “scattering” of T cells in alopecia areata [15].

6. Laser hair transplantation

Lasers have also been suggested as auxiliary devices for patients undergoing autologous hair transplantation, a common surgical option for patients with extensive hair loss. Starting in 1995, carbon dioxide laser tissue ablation was proposed as an effective way to generate implantation holes and slits because of its efficiency and ability to significantly decrease damage to surrounding tissue and recovery time [76, 77]. However, the carbon dioxide laser wavelength of 10,600 nm is in the far-infrared spectral region and can result in minor thermal damage to the scalp [78].

Patients with scarring or cicatricial alopecia, a diverse group of rare inflammatory disorders that ultimately result in permanent follicular damage and irreversible hair loss, often seek hair transplantation. Yet, because of low perfusion of the scarred recipient tissue in these patients, it is imperative that minimal trauma be done when creating implantation holes and slits [79]. The Erbium:YAG laser, with an infrared emission of 2940 nm, permits “cold” ablation with greater absorption and less thermal damage than the carbon dioxide laser system. One study found that using a fluence of 80-120 J/cm² and 8-12 pulses was particularly effective and resulted in a 95 percent mini- and micrograft survival rate [80].

7. Conclusions

Even though laser treatments for alopecia are currently available in a non-clinic setting, none are FDA-approved. Notably, no laser studies are currently available for telogen effluvium, but a group of hair loss experts believe that if laser devices are used in the pre- and post-surgical periods, the risk of post-surgical telogen effluvium may be minimized and an earlier regrowth of transplanted hair may be promoted [16]. A better understanding of paradoxical hypertrichosis after photoepilation can help design more effective lasers and target more appropriate populations with alopecia. For instance, the patient groups most susceptible to hypertrichosis with laser epilation, namely those with dark skin and/or darker, coarser hair, may be more likely to benefit from laser treatment. Additional mechanistic studies and large-scale randomized trials will help elucidate whether laser therapy can increase hair growth and/or prevent further hair loss for those living with alopecia.

ACKNOWLEDGEMENT: Sophia Rangwala gratefully acknowledges support from the North American Hair Research Society.


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