Long-pulsed Nd:YAG for Hair Removal: Early Histological Changes Carie T. Chui, MD., Roy C. Grekin, MD., Philip E LeBoit MD., and Christopher B. Zachary, FRCP Department of Dermatology, University of California, San Francisco, California 94115
Abstract: The use of the long-pulsed Nd:YAG laser for hair removal is currently being studied. It may offer advantages over some of the preexisting laser hair removal systems, especially in more darkly pigmented patients. Histologic examinations of biopsies taken after treatment demonstrate focal heat-induced damage to the hair follicle. Key words: Nd:YAG laser; hair follicle; hair removal; histology, intense pulsed light source © 1999 LaserNews.net, LLC
Many laser systems have been successfully utilized for hair removal, including the Qswitched Nd:YAG, the diode, the long-pulsed ruby and alexandrite lasers.  However, some these systems can be poorly tolerated in more darkly pigmented patients due to side effects of erythema, blistering, and post-inflammatory hyper or hypo-pigmentation. The wavelength of the Nd:YAG laser provides certain advantages in targeting hair follicles over the other systems. The longer wavelength leads to deeper penetration, enabling the energy of the laser to reach the hair bulbs and/or bulge located in the lower dermis. These follicular structures are the desired target since they are believed to be critical in hair regrowth.  The wavelength of the Nd:YAG also induces less energy absorption by other cutaneous structures, leading to less collateral damage and more efficient penetration. The decreased epidermal absorption accounts for the reduction in side effects seen with the Nd:YAG laser in darker skinned individuals.  Theoretically, the pulse duration of a hair removal laser should be shorter than the thermal relaxation time (TRT) of the hair follicle but longer than the TRT of the epidermis in order to maximize follicular damage while minimizing epidermal damage. This means that the ideal pulse width should be between 10-60ms. However, the Nd:YAG systems that have traditionally been used employ a Q-switched technology (either with or without the adjunct of a topical carbon-based solution to serve as a chromophore). The exact mechanism by which the Q-switched systems selectively destroy hair follicles is not well understood but probably relates to a photoacoustic event.  It is recognized that some patients having tattoo removal will notice coincidental permanent hair reduction in the treated areas. More recently, long-pulsed Nd:YAG lasers have been developed, combining the wavelength advantage of the Nd:YAG and the longer pulse duration advantage of the other long-pulsed systems. These include the Lyra by Laserscope and the CoolGlide by Altus. Only recently placed on the market, little clinical data on these new lasers is available at this time. A study of the Lyra using fluences of 100 J/cm2 for facial hair and 130 J/cm2 for non-facial hair and pulse duration of 30 msec showed successful reduction of hair growth at 3 months after a single treatment.  A study of the CoolGlide laser is also currently underway, using fluences of 50-60 J/cm2 and pulse widths of 15-30 msec.  Three month preliminary results show a 24-32% reduction in hair growth in treated sites compared with 8% in the control sites and minimal side effects. We have treated 20 patients with the Lyra, several of whom had with Fitzpatrick type IV and V skin. Short-
term follow-ups thus far suggest a good clinical response with minimal blistering and post-inflammatory pigment changes. The purpose of this brief article is to describe the histologic changes associated with the long-pulsed Nd:YAG laser. We observed histologic evidence for heat-induced follicular damage on punch biopsies taken 5-20 minutes following treatment with the Lyra. Treatment parameters included fluences of 60-100J/cm2 and pulse durations of 4050msec. Nuclear elongation and cytoplasmic degeneration at the outermost portion of the outer root sheath (often leading to separation from the adjacent vitreous membrane) at the level of the hair bulb was consistently found. (Fig. 1, 2, 3)
Fig. 1. Histologic findings from back of Type III patient minutes after treatment with the Lyra at 80 J/cm2 and 50 msec. Focal damage to the outer root sheath at the level of the hair bulb, leading to separation from the vitreous membrane (H&E original magnification 200X).
Fig. 2. Histologic findings from leg of Type IV patient minutes after treatment with the Lyra at 8 0 J / c m 2 and 50 msec. Elongated and degenerated cells of the outer root sheath with separation from the vitreous membrane (H&E original magnification 200X).
Fig. 3. Histologic findings from the same patient. Closer view of the elongated nuclei and degenerated cytoplasm of the outer root sheath cells (H&E original magnification 400X).
No significant histologic changes were noted in the surrounding collagen, epidermis, or rest of the hair follicle. The reason that this heat related damage is localized to this relatively non-pigmented area is unclear. However, the early, focal and limited nature of this damage does correspond with the comparative lack of reaction (consisting only of some temporary mild perifollicular edema) seen clinically. If lasting hair loss can be definitively established with the Lyra, the localization of the follicular damage suggests a role for this portion of the follicle in hair re-growth. A similar system, the Smart-Epil, which has been used in Europe, is also a longpulsed Nd:YAG laser for hair removal, but it differs from these newer systems by having a fixed pulse duration of 5 msec rather than a variable pulse duration of up to 60ms. One study using the Smart-Epil to treat 208 patients with fluences of 23-56 J/cm2 demonstrated long-term reduction in hair growth up to 6 months.  The treatments were well tolerated, and punch biopsies showed extensive necrosis of hair follicle 6 hours after treatment, as well as fibrosis and loss of hair follicles three months later. The contrast between these dramatic histologic findings compared with the subtle histologic changes which we observed may be related to the timing of the biopsies (6 hours compared with just 5-20 minutes after treatment), or to dissimilarities in the two laser systems. Whether this contrast will translate into a difference in long-term clinical response is yet to be determined. Clinical studies are needed to determine the efficacy of the new long-pulsed Nd:YAG lasers, and to compare them with other hair removal laser systems. However, it appears that long pulse 1064 nm lasers may provide an effective treatment alternative, one that may be better tolerated in more darkly-pigmented individuals. References and Links 1. 2. 3. 4. 5.
Dierickx C, Alora MB, Dover JS. A clinical overview of hair removal using lasers and light sources. Derm Clin 1999;17:357-66. Ross EV, Ladin Z, Kreindel M, Dierickx C. Theoretical considerations in laser hair removal. Derm Clin 1999;17:333-55. Littler CM. Hair removal using an Nd:YAG laser system. Derm Clin 1999;17:401-30. Goldberg DJ. Laser hair removal with a millisecond Q-switched Nd:YAG laser. Lasers Surg Med 1999; 11(suppl):22. Kilmer SL. 3 month clinical results using the CoolGlide long-pulse Nd:YAG laser for hair removal. (personal communication). Bencini PL, Luci A, Galimberti M, Ferranti G. Long-term epilation with long-pulsed neodimium: YAG laser. Dermatol Surg 1997;25:176-8.
Commentary David J. Goldberg, MD Skin Laser & Surgery Centers of New York & New Jersey, New Jersey Medical School
Lasers and light sources are successfully used to treat a variety of vascular and pigmented lesions. Only over the last several years has there been interest in the role of these technologies in the treatment of unwanted hair. The myriad hair removal technologies include ruby (694nm), alexandrite (755nm), diode (810nm), Nd:YAG (1064nm) lasers and intense pulsed light sources (590-1100nm). Although it has been assumed that all these systems
produce energy absorbed by melanin, the exact focus of damage within the hair follicle remains unclear. Long term hair removal requires that a laser or light source impact on one or more growth centers of hair. The major growth center has always been thought to be the hair matrix. However, as has now become quite clear, new hairs may, at least in animal models evolve from the dermal papilla, follicular matrix, or the "bulge". Although, it has generally been assumed that matrix cells, through their interactions with the dermal papilla, play a central role in follicular growth and differentiation, it has been noted that a complete hair follicle can be regenerated after the matrix-containing hair follicle is surgically removed. If the dermal papilla and not more than the lower one third of the follicle is removed, the hair follicle can regenerate. Oliver et al.1 have established that the outer root sheath and the adherent mesenchymal layer from the lower follicle are, in the absence of a matrix and dermal papilla, the essential elements in the regeneration of the hair follicle. It is in this light that the data of Chui, Grekin, LeBoit and Zachary becomes so important. The 1064nm wavelength used in their study has particular advantages over other utilized wavelengths because of its deeper penetration into the dermis with resultant potential deeper damage to the hair follicle. Such a wavelength may also be safer for darker complected individuals because of its poor absorption by epidermal melanin. McCoy et. al.,2 in a study somewhat similar to ChuiÕs study, have recently evaluated the histologic basis for ruby laser induced hair responses. They treated 24 subjects with a 3 msec ruby laser. All hairs were brown or black. There were 2 phases to the trial. In Phase 1 of the study, 15 of the 24 subjects were treated one time with five different fluences: 10 J/cm2, 15 J/cm2, 20 J/cm2, 30 J/cm2 and 40 J/cm2. Biopsies were undertaken either immediately after treatment, 1 week later or four weeks later. In Phase 2 of the trial the remaining 9 subjects were treated on three subsequent occasions with three different fluences: 20 J/cm2, 30 J/cm2 and 40 J/cm2. Representative biopsies were taken after one, two and three treatments. Phase 1, immediate post-treatment biopsies, showed damage to the hair shaft. The severity of damage appeared to be fluence related. Although cell viability appeared to be lost in the inner root sheaths, outer root sheaths remained viable at all fluences except 40 J/cm2 . The epidermis and dermis were unaffected at all utilized fluences. One-week biopsies showed changes consistent with those of early catagen. At one week, cellular death was noted in the outer root sheaths with pigment incontinence and degeneration of melanocytes. The severity of changes was fluence related. Telogen and vellus hairs appeared to have been unaffected by laser irradiation. Although the epidermis remained normal, the dermis now showed a low grade inflammatory infiltrate. At 4-week biopsies, follicular changes consistent with late catagen and early telogen stages of hair growth were noted at all treated fluences. At this point, the dermis had returned to normal. Phase 2 biopsies, performed 8 weeks after one treatment, revealed both terminal and vellus hairs at all utilized fluences. Although the terminal hairs were noted to be in either the anagen or late catagen/telogen stages, more hairs were in this second phase than would normally be expected. These findings were similar at all utilized energies. At six weeks after two treatments, separated by 12 weeks, findings consistent with cystic dilatation and terminal hair plugging of the infundibulum were noted. The deeper dermis revealed follicles in both telogen and anagen. No hair shafts were noted to protrude from the follicular orifices. After three treatments, six-week biopsies showed all terminal hairs to be in late catagen/early telogen or in early anagen phases. The authors postulated that the progressive histologic changes, seen after repeated treatments, are consistent with the improved clinical results seen after several treatments. McCoyÕs findings would suggest that although damage to the external root sheath may be mandatory to induce permanent changes in hair, it is also consistent with the findings seen in a hair as it enters the catagen stage of hair growth. It may be assumed, then that repeated treatments with a 1064nm Nd:YAG laser may lead to similar changes as those seen by
McCoy after repeated ruby laser sessions- without the same risk of epidermal melanin damage. We are currently evaluating the 48-72 hour histologic changes of millisecond Nd:YAG laser in a study looking at a variety of fluences including higher fluences than those utilized in ChuiÕs study. Chui, Grekin, LeBoit and Zachary are to be commended for their study. It is only with a better understanding of hair biology and the histologic evidence of laser induced changes that we will begin to truly understand the mechanism, of laser induced hair removal. Such studies are mandatory if laser hair removal is to grow as one of the most exciting areas of cutaneous laser surgery.
References 1. 2.
Oliver RE. Ectopic regeneration of whiskers in the hooded rat from implanted lengths of vibrissa follicle wall. Embryol Exp Morphol 1967;17:27-34. McCoy S, Evans A, James C. Histological studies of hair follicles treated with a 3-msec pulsed ruby laser. Lasers Surg Med 1999; 24: 142-150.