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  • Mechanisms of Laser Hair Removal: Could Persistent Photoepilation Induce Vitiligo or Defects in Wound Repair?

    KLAUS SELLHEYER, MD�

    BACKGROUND Current laser hair removal modalities achieve a long-term but not persistent (irrevers- ible) hair loss.

    OBJECTIVE This review highlights the mechanisms of the current laser hair removal technology and explores possible side effects.

    METHODS The literature is reviewed.

    RESULTS The hair shaft plays a key role in the mechanisms underlying current photoepilation proce- dures by acting as a vector for heat transfer. Together with inherent properties of the hair growth cycle and the anatomic specifics of the follicular stem cells located in the bulge, the crucial role of the hair shaft and its lack of complete destruction with present technology are also likely culprits for the non- persistent nature of present laser hair removal. Future persistent photoepilation may be associated with vitiligo or vitiligolike changes. Disturbances in wound repair of previously lasered sites are less likely.

    CONCLUSIONS The currently available laser hair removal protocols are safe, not the least because they achieve long-term but not persistent epilation. The adverse effects of persistent laser hair removal technology possibly available in the future are potentially problematic.

    Klaus Sellheyer, MD, has indicated no significant interest with commercial supporters.

    Laser hair removal is popular and relatively freeof adverse effects.1 A recent evidence-based meta-analysis, however, from January 2006 of a

    total of 30 published trials employing ruby, alex-

    andrite, diode, and Nd:YAG lasers as well as intense

    pulsed light concluded that there is no evidence of

    complete and persistent hair removal with present

    technologies.2 Many patients request a persistent

    photothermolysis solution for their unwanted hair.

    Although such a desire on the patients’ behalf is

    understandable, a cautious approach to persistent

    hair removal is prudent. Based on recent basic sci-

    ence data on the location of the melanocyte stem

    cells,3–8 there is a concern that total destruction of

    the hair follicle may possibly induce vitiligo or viti-

    ligolike changes. There is also a concern with defects

    in subsequent wound repair to the sites of previous

    laser hair removal should the keratinocyte stem cell

    population in the hair follicle bulge9,10 be destroyed.

    This review will explore the rationale for these

    concerns from a clinical, histopathologic, and basic

    science perspective. To that extent, the article will

    initially explore the mechanisms of laser-induced

    photoepilation, which is permanent but not persis-

    tent, and later this review will address these concerns.

    Permanent but Not Persistent

    The term ‘‘hair removal’’ is understood differently by

    the lay public and the scientific community, and even

    inside the latter it is often used inconsistently. The US

    Food and Drug Administration has adopted a def-

    inition for permanent hair removal as a ‘‘significant

    reduction in the number of terminal hairs after a

    given treatment, which is stable for a period of time

    longer than the complete growth cycle of hair

    follicles at the given body site.’’11 This definition of

    ‘‘permanent’’ departs from the original meaning

    of its Latin root (‘‘permanentem,’’ preposition of

    ‘‘permanere’’ = ‘‘endure, continue, stay to the end’’)

    & 2007 by the American Society for Dermatologic Surgery, Inc. � Published by Blackwell Publishing � ISSN: 1076-0512 � Dermatol Surg 2007;33:1055–1065 � DOI: 10.1111/j.1524-4725.2007.33219.x

    1 0 5 5

    �Departments of Dermatology and Pathology, The Cleveland Clinic Foundation, Cleveland, Ohio

  • and does not imply that the laser-induced hair loss is

    irreversible. It is this definition of the term ‘‘perma-

    nent’’ which leads to patient misconceptions. In the

    following discussion, the term ‘‘persistent’’ (from

    Latin ‘‘persistere’’ = ‘‘continue steadfastly’’) will be

    used as a reference to hair that does not regrow

    subsequent to laser hair removal. So far all laser-

    based epilation procedures may be long-term but are

    followed by regrowth of hair at one point in time.11

    They are therefore permanent in the sense of the

    above definition but not persistent.

    Mechanisms of Current Permanent Laser Hair

    Removal: Primary Damage to the Hair Follicle

    Epithelium or Heat Conduction via the

    Hair Shaft?

    The approach of laser hair removal is less specific

    compared to laser therapy of tattoos or telangiec-

    tasias in which the target represents a specific

    chromophore, absorbing the laser light in a wave-

    length- and time-specific manner, which produces

    destruction of the target (for review see Goldman12).

    Although photoepilation also targets pigment, the

    targeted pigmentFmelaninFfunctions only as a

    mediator of heat dissipation to the surrounding

    tissue. Within the anagen hair follicle, melanin is

    present in the melanocytes of the hair matrix

    (Figures 1 and 2D) and in the hair shaft (Figures 2A

    and 3). For epilation to occur, the laser can only

    target follicles that are pigmented. Thus, hair folli-

    cles that are less pigmented (blond) as well as those

    pigmented with pheomelanin-containing (red) in-

    stead of eumelanin-containing (dark) hair are less

    susceptible to photoepilation procedures.13–19

    Laser hair removal based on the theory of selective

    photothermolysis20 was first attempted in human

    subjects in 1996.21 Multiple clinical studies on a

    variety of laser systems followed (for review see

    Haedersdal and Wulf,2 Dirieckx,11 Dierickx et al.,22

    Anderson,23 Lepselter and Elman,24 and Wanner25).

    Unfortunately, histologic data on laser hair removal

    are often based on only a few subjects (see below).

    Large series with systematic histologic evaluations

    over a long time course following laser epilation are

    not available. In addition, data are also often difficult

    to compare because different laser types and different

    treatment parameters are employed. Nevertheless,

    two theories of how laser light achieves hair removal

    can be crystallized from the published histologic data.

    The first theory emphasizes on a direct effect of the

    laser light on the viable follicular epithelium, com-

    posed of the inner and outer root sheath with the

    keratinocyte stem cell–containing bulge, as well as

    on the follicular papilla made up of specialized fi-

    broblasts (Figure 3). Grossman and colleagues21 re-

    ported histologic damage to the follicular epithelium

    with increased eosinophilia and nuclear elongation,

    leading to follicle rupture in isolated areas, after

    normal-mode ruby laser pulses at 270 ms and using a 6-mm beam diameter. Similar changes were noted

    Figure 1. The pigmented follicular melanocytes (arrow) are located among the hair matrix keratinocytes and transfer their melanin into the hair shaft. The follicular papilla inva- ginates the epithelial portion of the hair bulb at the bottom. The hair shaft is not depicted in this micrograph. The tan- gentially cut outer root sheath (clear cells in the upper cen- tral portion of the hair follicle) is shown instead. Original magnification, �250.

    D E R M AT O L O G I C S U R G E RY1 0 5 6

    L A S E R H A I R R E M O VA L

  • after Nd:YAG laser radiation of hair.26 In a study

    by McCoy and coworkers,15 the ruby laser at dif-

    ferent fluences resulted in damage to the hair follicle

    specifically in the inner root sheath. Even at the

    highest fluences, there was no evidence of total fol-

    licular dropout and the follicular papillae remained

    viable.15 More extensive damage to hair follicles

    after ruby laser application (1-ms pulses, up to

    0.9 Hz, 5-mm spot size) with detachment of the

    outer root sheath from the surrounding fibrous

    root sheath initially and eosinophilic degeneration

    of the inner root sheaths later were reported in eight

    Japanese patients.27 Three studies, one of which

    employing lasered ex vivo scalp skin from face-lift

    operations,28 describe damage to the keratinocyte

    stem cell–containing bulge region of the hair follicle

    after ruby28,29 as well as alexandrite laser.30

    The evidence for this claim, however, seems weak

    Figure 2. (A) The bulge (arrow), here from a follicle of the bulbous hair peg stage of a human embryo, is typically more easily discernible during development compared to the adult hair follicle. The arrowhead marks the outer root sheath. Note that the centrally located hair shaft is already melanized (reproduced with permission from Sellheyer K, Bergfeld WF. Histopathologic evaluation of alopecias. Am J Dermatopathol 2006;28:236–5947). (B) Melanocytes (arrow- heads) are found in the bulge from this human fetus at ge- stational week 20. They are labeled with an antibody against the Bcl-2 protein. The Bcl-2 protein is an antiapoptotic pro- tein protecting the melanocytes from cell death. (C) In this HMB-45–labeled bulge melanocyte (arrow) from another human fetus the