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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
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�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
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