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Biological and clinical aspects in laser hair removal
Introduction
Excess hair and/or unwanted hair are of significant
medical, social and cultural importance and are there-
fore the subject of much attention, manipulation and
regard in both genders and all races. The multitude
of treatments available is testimony to these facts.
Traditionally, conditions such as hirsutism, hypertri-
chosis, and cosmetic elegance have been treated with
electrolysis/thermolysis, tweezing, shaving, waxing and
sugaring, plucking, threading, depilatories and X-ray
therapy.
1
These methods, however, were found to be
slow, tedious, painful, impractical for treating large
areas, and, in most cases, temporary. Consequently, the
need for a long-term, non-invasive, rapid, reliable and
safe method became a necessity in our society.
When first described some 7 years ago, laser hair
removal created controversy.
2
As the technology
matured, laser hair removal generated growing
demand not only for a safe, non-invasive, pain-free
procedure, but also for effective, rapid pace, easy to
operate, and affordable technology. Today, photoepila-
tion by laser and other light-based technology is the
fastest growing procedure in modern cosmetic derma-
tology. As more clinical research and experience is
gained in the field of laser hair removal, manufacturers
and practitioners have been obligated to seek safer and
more effective results.
Although the technology is relatively new, it has
already generated much interest among clinicians and
patients alike because of its ability to delay hair
regrowth, and non-invasively remove large areas of
J Lepselter
1
and M Elman
2
1
Msq P.O. Box 3021, Caesarea 38900,
Israel;
2
Dermatology and Lasers Clinic,
21 Leonardo Devinci Street
Tel-Aviv, 64733 Israel
INTRODUCTION: In the past cen-
tury, unwanted hair has been
traditionally treated with multi-
tudes of techniques that were
found to be slow, tedious, painful,
impractical, and resulted in poor
long-term efficacy. Consequently,
there has been a public demand
for a novel, rapid, reliable, safe,
and affordable hair removal tech-
nique. In the last decade, laser and
light-based technology for hair
removal became one of the fastest
growing procedures in modern
cosmetic dermatology.
OBJECTIVE: To discuss the latest
scientific and clinical issues in the
field of photoepilation as evolved
in the past decade: hair biology,
laser physics and skin optics, tech-
nology and clinical experience.
RESULTS: From substantial clinical
experience, it becomes apparent
that in the ideal subject with fair
skin and dark hair, a single treat-
ment can reduce hair by 10–40%;
three treatments by 30–70%; and
repeated treatments by as much as
90%. These results persist for as
long as 12 months. Diffuse and
perifollicular cutaneous erythema
and pigmentary changes are the
most common adverse side effects.
Most complications are generally
temporary.
CONCLUSIONS: Photoepilation,
when properly used, offers
clear advantages when compared
with older, traditional techniques.
Although an ever-increasing num-
ber of published studies have con-
firmed the safety and short and
long-term efficacy of photoepila-
tion, the technology still has limits
and risks. (J Dermatol Treat (2004) 15:
72–83)
Received 7th July 2003
Accepted 14th November 2003
Keywords: Anagen — Bulb — Follicular erythema — Hair follicle — Laser
Correspondence:
Joseph Lepselter, PhD, Msq PO Box 3021, Caesarea 38900, Israel. Tel
z972 4 627 5357; Fax z972 4 627 5368; E-mail: lepselt@bezeqint.net
Journal of Dermatological Treatment (2004) 15, 72–83
#2004 Journal of Dermatological Treatment. All rights reserved. ISSN 0954-6634
DOI: 10.1080/09546630310023152
72
hair with minimal discomfort, and a low incidence of
complications.
3
However, efficacy and safety of hair
removal by laser and light-based technology varies
considerably among manufacturers due to differences in
patients’ skin–hair biology traits, optimization of electro-
optical parameters and clinical protocols.
The purpose of this review is to discuss the major
scientific and clinical issues in the field of photoepilation
that have evolved in the last decade. Pertaining to our
discussion will be the following topics: hair biology;
biomedical optics and laser physics; clinical experience
with selected technologies; and essential issues in
photoepilation.
Hair biology
A hair follicle consists of three regions: the infundibu-
lum, isthmus, and hair bulb. The general anatomy of
hair follicle is shown in Figure 1. The inferior segment of
the hair follicle lies below the arrector pili muscle
insertion and includes the hair bulb and dermal papilla.
As will be discussed later, this area is of great impor-
tance in photoepilation. On average, the bulb is appro-
ximately 4 mm in depth from the surface of the skin, a
considerable depth of penetration required by the laser
light-based systems.
4
The hair bulb is made up of germi-
native matrix cells along with interspersed melanocytes.
The dermal papilla, located in the base of the bulb, is fed
by the bloodstream, which carries nourishment to produce
new hair. The bulge is located approximately one-third of
the distance down from the skin surface to the follicle bulb.
Dermal sheath cells and epidermal outer root cells are
found in the follicle bulb. These cell types extend into the
isthmus and infundibulum of the hair follicle and play an
important role in hair growth.
5,6
Human hair grows in a cyclic pattern. The cycle
consists of a growth or anagen phase followed by
intermediate degradation of a portion of the follicle,
known as the catagen phase and then by a resting
period when no growth occurs – the telogen phase.
7
Figure 2 describes the three phases of the hair growth
cycle. It appears that different areas of the body, in
addition to having shorter anagen cycles, have varying
percentages of hairs actually in the anagen phase.
The anagen duration varies greatly depending on age,
season, gender (anagen in thigh hair in men is 54 days
versus 22 days in women), body site, hormones and
underling genetic susceptibilities.
8
The catagen phase is
generally 3 weeks in duration whereas the telogen
phase usually lasts approximately 3 months. At any
given time, the majority of the hair follicles (80–85%)
are in the anagen phase and the remaining follicles are
either in the catagen phase (2%) or the telogen phase
(10–15%).
9,10
Table I shows the duration and percen-
tage of the hair cycle in relation to body areas.
For effective hair removal a laser/light source should
damage one or more growth centers of hair, and the
pluripotential cells of the bulge, dermal papilla, and hair
matrix must be treated in the anagen cycle. It is during
the anagen phase that melanin production occurs and
becomes part of the growing follicle. It is also in the
anagen phase that damage can affect the structure
theoretically responsible for hair generation. During the
telogen phase, the dermal papilla moves upward toward
the bulge region and stimulates the onset of the anagen
phase. In this active growth phase, the papilla moves
down away from the bulge mass and the hair matrix
cells regress during the catagen phase. Thus, depending
on the stage of the hair cycle, the distance between the
bulge region and the dermal papilla varies along with
the depth of the dermal papilla within the dermis. These
structures represent targets for hair follicle damage, and
relative movement with respect to the skin structure
attenuate their photothermal susceptibility to a fixed
wavelength laser beam. Thus, to achieve long-term hair
removal, it is essential to destroy the structures that are
responsible for hair growth: the bulge and bulb.
11
Laser physics and skin optics in
hair removal
Laser hair removal is a multifactorial process that involves
complex photothermal reaction via the epidermis–dermis
Figure 1
Hair follicle anatomy in photoepilation.
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
73
matrix, aimed to cause hair follicle damage while sparing
the epidermis. Thus, hair follicle eradication bya laser light
source is a function of various laser (e.g. power, spot size,
irradiation time and repetition rate) and tissue (absorption
and scattering coefficients, density, heat capacity and
thermal conductivity) parameters.
12
The laser source may be continuous mode or pulsed.
A continuous mode laser emits a continuous stream of
light as long as the medium is excited, resulting in
heating and vaporization of the target tissue. Alterna-
tively, a pulsed laser will emit light only in short
amounts, which may vary from nanoseconds to as long
as seconds. Various sources of laser/light-based technol-
ogy exist, including continuous light, flashlamp, radio
frequency, high-voltage discharge, diodes and others.
When the lasing medium is excited, the molecules are
stimulated to a higher energy level. These excited
molecules tend to decay spontaneously to their original
lower energy level realizing a photon. All emitted
photons bear a constant phase relationship with each
other in both time and phase – coherency. In turn, all
laser light photons travel in the same direction with low
divergence – collimated. Finally, laser light has high
irradiance, since all the light is concentrated into a
narrow spatial band resulting in a high radiant power
per unit area.
Energy refers to the number of photons delivered and
is measured in joules ( J). Power is measured in watts
(W) and refers to the delivery rate of energy (1 W=1 J/s).
Fluence is the total energy delivered per unit area and is
measured in J/cm
2
. Pulse duration is the amount of time
laser energy is applied (ns, ms). The pulse frequency is
measured in hertz (1 Hz=1 pulse/s). Wavelength is
measured in nanometers (nm) and refers to the distance
between the peaks of the light waves and is used to
characterize the type of light (green, red, yellow).
The technology employed for hair removal by lasers/
light-based systems is based on the principle of selective
Figure 2
Hair follicle cycle. (A) Anagen phase: hair matrix cells migrate outward from the shaft and the melanin load is at its highest. (B) Catagen
phase: the follicle detaches from the papillae and contracts – eventually falling out. (C) Telogen phase: mitosis ceases, the hair matrix
regresses and the papilla retracts to a place near the bulge (apoptosis).
Body area Anagen hair (%) Telogen duration Density (cm
2
) Follicle depth
Scalp 85 4 months 350 3–5 mm
Beard 70 10 weeks 500 2–4mm
Moustache 65 6 weeks 500 1–2 mm
Armpits 30 3 months 65 3–4mm
Bikini line 30 3 months 70 3–4 mm
Legs 20 4 months 60 2–3 mm
Table I
Duration and percentage of hair in the anagen and telogen phase (ref. 9)
74
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
photothermolysis. According to this principle, selective
thermal destruction of a target will occur if sufficient
energy is delivered at a wavelength well absorbed by the
target within a time period less than or equal to the
thermal relaxation time (TRT) of the target.
12
The TRT
is the time it takes for the target to cool (half of its
baseline temperature) and transfer the heat to sur-
rounding structures. Under these conditions, it is
possible to selectively target structures (e.g. hair follicle)
while sparing the surrounding structures or tissues. The
target site for the selective destruction of hair follicles
can either be endogenous melanin or exogenous
chromophore.
A corollary of selective photothermolysis is thermo-
kinetic selectivity. This theory proposes that for the
same chromophore, a longer pulse duration allows
intrapulse cooling of smaller targets more rapidly than
larger targets. Longer pulse durations are predicted to
limit thermal damage to the epidermis. If the pulse
duration exceeds the thermal relaxation time of the
basal cell layer (about 0.1 ms) or entire epidermis (about
10 ms), these structures will cool as they are heated
during the laser pulse. In other words, larger targets
(hair follicles) can be selectively injured more than
smaller targets of the same chromophore (epidermis).
13
Recently, a novel concept of laser hair removal uses
the thermal damage time (TDT) rather than the
traditional hair follicle TRT concept that has been
described. Studies indicate that the ideal pulse duration
for medium to coarse hair reduction may be longer than
the TRT of the hair follicle. Since the melanin occupies a
much smaller volume compared with the follicle, heat is
conducted from the shaft and melanized portion of the
bulb to surrounding structures according to the laws of
thermal diffusion. It has been suggested that widening
the pulse duration allows an increase in the threshold of
epidermal damage. As we have learned more about the
mechanism of hair removal, it has become evident that
the true targets for permanent hair removal are located
at a distance from the hair shaft, at the outer root
sheath of the follicle (stem cells), and the base of the
follicle. This important observation has required recon-
sideration as to the appropriate laser parameters,
particularly pulse width and energy density.
14–16
When considering photothermal destruction of hair
follicles, there are three parameters that need to be
considered: wavelength, pulse duration, and fluence.
The longer the wavelength, the deeper the laser light
penetrates the skin. To damage hair follicles, laser light
must be absorbed by a chromophore within the follicle.
Most lasers target the endogenous chromophore mela-
nin within the pigmented hair shaft by delivering red or
near-infrared wavelengths. Melanin is the primary light
absorber in the optical window between 600 nm and
1100 nm. Wavelengths in this range are poorly absorbed
by competing chromophores such as hemoglobin and
water and penetrate deeply into the dermis.
17
It should
be remembered though that the absorption of light by
melanin decreases with longer wavelengths and that
oxyhemoglobin and melanin have similar absorption at
wavelengths at 750–850 nm.
The ability of these wavelengths to damage hair
correlates directly with the amount and type of melanin
within the follicle: pheomelanin and eumelanin. Dark
hair that contains large amounts of eumelanin readily
absorbs these wavelengths and is most susceptible to
laser-induced damage.
18
In theory, the use of longer
wavelengths increases the ratio of energy deposited in
the dermis to the epidermis, which results in relative
bulb heating and epidermis sparing. However, although
there is more melanin absorption at a wavelength of
755 nm than 800 nm, larger energy density (fluence)
must be employed during 800 nm than with a 755 nm
wavelength laser. In the case of brown and black hairs,
where the target chromophore is eumelanin, long-
pulsed diode lasers at a wavelength of 800 nm were
found to be safe and clinically effective.
19
The necessary energy density (i.e. fluence) for the
coagulation of hair follicle is proportional to the hair
shaft diameter, as long as the bulb and follicle thickness
are proportionate to hair shaft diameter; the thinner the
hair, the smaller the energy density level.
20
In general,
the fluence of the laser should be greater than or equal
to the threshold fluence for tissue destruction. To
confine thermal damage to the hair follicle, the laser
pulse duration should lie between the TRT for epidermis,
which is approximately 3–10 ms, and the TRT for the
hair follicles which is approximately 40–100 ms. Using
this concept to deliver light of the right combination of
wavelength, energy fluence, and pulse duration, it is
possible to precisely target the hair follicle and improve
long-term hair removal.
The laser pulse width plays an important role in
determining selective photothermolysis. High energy,
short pulses of laser light cause extremely rapid heating
of the target, with a rapid expansion of the thermal
plasma. If the pulse width is too long, however, there
will be insufficient time for the heat to dissipate, and
undesirable temperature increase will occur with ther-
mal injury to non-follicular structures, which could
result in scarring or irregularities in pigmentation.
21
Ideally, the spot size should be as large as possible
to reduce scattering of the light. When light is applied
to the skin using a small spot size, the scattering of
photons diffuses the beam rapidly. The fluence decays
very quickly as a function of depth, so that most of the
energy is dissipated in radial directions (outwards) and
cannot reach the hair bulbs. With a large spot size,
light penetration is more efficient since the ‘source’ of
photons has an almost planar geometry. In human skin,
about 15–20% of incident light at 700 nm penetrates to
a depth of 3 mm. Thus, by using a larger spot size
scattering of light in the dermis is lessened, leading to a
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
75
greater depth of penetration and a lower threshold
fluence.
22
Clinical experience
Since the first laser-assisted hair removal device was
cleared in 1995, more than 15 laser systems have been
approved by the Food and Drug Administration (FDA) to
specifically target hair follicles.
23
These systems include
ruby (694 nm), alexandrite (755 nm), diode (800–
1000 nm), Q-switched and long-pulsed neodymium:
yttrium-aluminum-garnet (Nd:YAG; 1064 nm) and
intense pulsed light (IPL) sources (550–1200 nm).
Devices that target exogenous chromophores are carbon
particles plus Q-switched Nd:YAG laser (1064 nm) and
5-aminolevulonic acid. A summary of different com-
mercially available hair removal devices is presented
in Table II.
Normal-mode ruby laser (694 nm)
The pulsed ruby laser was the original system used to
perform melanin-based selective photothermolysis of
hair. The ruby laser delivers red light at a wavelength
of 694 nm. Three ruby lasers have been approved by
the FDA for hair removal: EpiLaser/E2000 (Palomar);
EpiPulse (Sharplan/ESC); and RubyStar (Aesculap
Mediteo). Because of the high melanin absorption at
694 nm, ruby lasers are most useful for light-skinned
(Fitzpatrick skin types I–III) individuals with dark hair.
In a recent study, Allison et al studied the long-term
hair regrowth in three patient groups: top lip (n=25),
axillae (n=25) and legs (n=9). Two treatments were
given on the right and left sides at monthly intervals. A
third treatment was given randomly to one side. Hair
counts of the experimental sites were made at monthly
intervals for 1 year. Long-term hair reduction was
achieved in all patients. A single treatment reduced hair
counts by up to 75%. Three treatments had an impact
for 2 additional months, but not long term. Unexpected
spontaneous hair reduction was found 5 months
following treatment and lasted 2 months. This ruby
laser produced a persistent two-thirds reduction in hair
count over 8 months of follow-up and no significant
regrowth follow-up to 12 months.
24
Studies with short-
term follow-up have observed 37–72% reduction at 3
months after one to three treatments, to a 38–49% hair
reduction 1 year after three treatment sessions.
25,26
In a long follow-up study, Grossman et al studied 13
patients with fair skin and dark hair. Patients were
treated once on the thighs or back at fluences of
20–60 J/cm
2
and pulses of 270 msec. In all subjects, hair
regrowth was delayed for 1–3 months at all fluences.
A complete regrowth was present in five out of 13
patients. At 1–2 years follow-up, four of the seven
patients had persistent hair loss, which was greatest in
the sites treated with the highest fluence.
27
Chana and Grobbelaar
28
prospectively assessed the
long-term results of ruby laser depilation in 346 con-
secutive patients who underwent hair removal at 402
anatomical sites. The patients were treated using a
ruby laser, with the mean power ranging from 8.6 J to
15.7 J according to skin type. Results were assessed
using two outcome measures: the percentage reduction
in hair density and the hair-free interval. The median
reduction in hair density was 55% (range 0–100%) at a
median time of 1 year after the last treatment session.
The median hair-free interval was 8 weeks. Patients
underwent a median number of four treatment sessions.
Forty-three of the 346 patients were treated at more
than one anatomical site. Of the sites treated, a 75%
reduction in hair density was achieved in 22%, 90%
reduction was achieved in 2.2%, and complete depila-
tion was achieved in only 0.7%. Darker colored hair
was more effectively treated. Treatment efficacy was not
affected by anatomical site, with the exception of the
faces of male patients, which were found to be par-
ticularly resistant to treatment. There was a significant
correlation between the number of treatments given and
the outcome. The overall complication rate was 9.0%
(36 of 402 sites) with respect to pigmentary changes
and blistering, but varied according to Fitzpatrick skin
type. The complication rate was highest in skin types V
Laser
Wavelength
(nm)
Pulse duration
(ms)
Fluence
(J/cm
2
)
Spot size
(mm)
Repetition rate
(Hz) Cooling mean
Mythos-500 (Msq) 810 0–400 5–120 10612 up to 4 Sapphire contact
Q-switched Nd:YAG (Thermolase) 1064 10
x5
2–3 7 10 Not needed
Long-pulsed ruby (Palomar) 694 3 10–40 10 1 Sapphire contact
Long-pulsed alexandrite (Cynosure) 755 5, 10, 20, 40 5–50 10–15 up to 2 Cold air flow
LightSheer (Star/Coherent) 810 5–100 10–60 12612 up to 2 Sapphire contact
Long-pulsed Nd:YAG (Laserscope) 1064 1–50 up to 150 1–4 up to 4 Contact cooling
Super-long-pulse 1000 (Palomar) 810 200–1000 up to 100 10 up to 3 Contact cooling
Laser/light source 550–1200 15–100 up to 45 10645 0.5 Circulating cooling
8633
Table II
Parameters of selected hair removal lasers and light sources
76
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
and VI (24.7%), with no complications in skin type I.
Although a greater than 50% reduction in hair density
was achieved in half of the 346 patients treated,
complete depilation was achieved in only an extremely
limited number of patients. In other controlled studies,
the ruby laser (one to four sessions) proved to be more
efficacious for hair reduction than shaving or waxing
only.
29,30
Alexandrite laser (755 nm)
The alexandrite laser allows greater depth of penetration,
making it relatively safe in darker-skinned (Fitzpatrick
skin types I–IV) individuals. However, melanin absorp-
tion is somewhat less at the wavelength of alexandrite
(755 nm) when compared with the ruby (694 nm).
Alexandrite lasers for hair removal were cleared by
the FDA to market in the USA in 1997. EpiTouch Alex
(ESC Sharplan Medical Systems), GentleLASE (Candela
Laser Corp.), and Photogenica LPIR (Cynosure, Inc.) are
currently available.
The reported success rate of hair removal using the
alexandrite has ranged from 40% to 80% at 6 months
after several treatments. In a controlled randomized
study, McDaniel et al showed a 40% to 56% reduction
of hair growth at 6 months after one treatment with a
variable-pulsed alexandrite laser on the lip, leg, and
back.
31
This study found that one treatment with a
variable-pulsed alexandrite laser produced maximum
hair regrowth reduction at 6 months of 40–56% for the
lip, leg and back. Sites treated with a 10 ms pulse
duration were found to have a significantly better hair
reduction rate that those treated with 5 ms or 20 ms
pulse widths.
Laughlin and Dudley found an average of 43%
reduction at 6 months plus ‘one growth cycle’ after a
single treatment at the bikini line, with 60% of sites
having greater than 30%.
32
An uncontrolled study,
using a uniform protocol, demonstrated a mean of 74%
hair reduction 1 year after five treatment sessions at the
bikini line. The average patient had a 78% clearance of
hair noted at 1 year with no evidence of scarring or
pigmentary changes.
33
In 150 dark-skinned patients (skin types IV–VI)
treated with the alexandrite laser (18 J/cm
2
, 40 ms),
side effects occurred in about 2% of cases.
34
Some
studies have shown that the 20 ms pulse duration
reduces the risk of epidermal damage and pigmentary
alteration, but treatment is more painful when longer
pulse durations are used.
35
Diode laser (800–1000 nm)
Diode lasers for hair removal were cleared by the FDA to
market in the USA in 1997. Because of the longer
wavelength, the active cooling, and the longer pulse
widths, individuals with darker skin can be treated more
safely with this system. In general, the diode laser
system has been found to be better tolerated by patients
with darker skin types (V–VI) than the ruby laser.
Overall, clinical studies with the diode laser system
have reported variable success rates ranging from 65%
to 75% hair reduction at 3 months after one to two
treatments with fluences of 10–40 J/cm
2
,tow75% hair
reduction in 91% of individuals 8 months after three to
four treatments at 40 J/cm
2
.
36
In a recent study, Fiskerstrand and colleagues
15
compared two systems (side-by-side study) with different
pulse structures. The radiant exposure was selected to a
value of 35 J/cm
2
, which is frequently used in the clinic
in accordance with the manufacturer’s recommenda-
tions. Twenty-nine patients with hair color ranging
from light brown to black on the upper lip were studied.
Three treatments were performed at 6–8 week intervals.
The percentage hair reduction and acute and long-term
side effects were evaluated after treatment. The average
hair reductions 6 months after the first treatment were
similar in both diode systems (49% and 48% clearance).
No scarring or pigmentary change of the skin was
observed after any of the treatments with either laser.
However, differences in acute side effects such as degree
of erythema and burned hairs were observed. No stati-
stically significant differences in hair removal efficacy
were observed.
Rogachefsky et al
14
have evaluated the clinical effi-
cacy and side effect profile of a modified 810 nm diode
laser device operating in a super-long-pulse mode (200–
1000 ms). Ten female subjects with Fitzpatrick skin
types I–VI received either one or two laser treatments at
eight test sites. Super-long-pulse durations of 200–
1000 ms were evaluated with delivered fluences ranging
from 23 to 115 J/cm
2
. Subjects were followed for 6
months after the first treatment. The clinical results
show that safe hair removal in all skin types can be
accomplished with an 810 nm diode laser delivering
super-long-pulse durations. Pain and complications
were greatest at the highest pulse duration (1000 ms)
and the highest fluence (115 J/cm
2
). Optimal hair
reduction at 6 months (31%) was achieved at a thermal
diffusion time of 400 ms (46 J/cm
2
).
Dierickx et al evaluated the effectiveness and safety in
ninety-five subjects with dark hair (Fitzpatrick skin types
I–IV). Subjects were treated at baseline and 1, 3, 6, 9,
and 12 months after treatment. One versus two treat-
ments were compared. Treatment results demonstrated
both hair growth delay (in all patients) for 1–3 months
and permanent hair reduction of 46% (40 J/cm
2
;20ms
pulse width).
37
Several other studies have demonstrated the efficacy
of the diode laser hair removal. In one study of
50 patients, quantitative hair counts performed for 9
months after treatment showed long-lasting and pos-
sibly permanent hair loss.
38
Lou et al who looked at
light-skinned patients with a single session, detected a
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
77
significant regrowth rate ranging from 65% to 75% 20
months after treatment. Two-session treatments were
associated with a longer growth delay, ranging from
47% to 66%.
39
Sadick et al studied 24 female subjects
(skin types II–IV) were treated three times at monthly
intervals with a new 810 nm diode laser (spot size
12 mm, pulse width 50 ms, fluence 25–35 J/cm
2
). A
mean hair removal efficiency of 74% and 79% was
noted at 3 and 6 months, respectively.
40
Nd:YAG laser (1064 nm)
The Q-switched 1064 nm Nd:YAG laser with or without
topical carbon suspension was one of the first laser
systems used to remove hair. The poor absorption by
melanin at this wavelength coupled with an epidermal
cooling device makes the long-pulsed Nd:YAG laser a
safe treatment option for patients with the darkest skin
phototypes (III–VI) and, therefore, for darker Fitzpatrick
skin types the long-pulsed Nd:YAG is preferred to the
ruby laser. However, because of reduced absorption by
follicular melanin, very high fluences (50–100 J/cm
2
)
are required to damage pigmented hair follicles.
Theoretical considerations to improve the performance
of the Nd:YAG laser have been proposed, including an
improvement in the exogenous chromophores used.
In addition, the Nd:YAG laser may be useful in the
treatment of light hairs, when used with the topically
applied carbon suspension. Most of the Nd:YAG systems
are Q-switched, with pulses ranging from 10 ns to
30 ms, although Nd:YAG equipment delivering non-Q-
switched long pulses is also available. Several long-
pulsed Nd:YAG lasers have been approved by the FDA
for hair removal or laser treatment of darker skin types.
Overall, clinical studies have demonstrated less hair
reduction with the Nd:YAG laser compared with those
results published with the ruby or alexandrite lasers. In a
recent study, Rogachefsky et al
41
evaluated the efficacy
of a long-pulsed Nd:YAG laser system. Twenty-two
subjects were treated with a cryogen spray-cooled long-
pulsed Nd:YAG laser. Four adjacent sites were assigned
to each subject, and were treated with parameters of
50 J/cm
2
with a 25 ms pulse duration; 60 J/cm
2
with a
50 ms pulse duration; 80 J/cm
2
with a 50 ms pulse dura-
tion; and control. Hair counts were obtained immediately,
and 1 week, 1 month, and 3 months after treatment, and
multivariate regression analysis was used to determine
the significance of hair reduction. At 3 months, the
higher settings of 60 J/cm
2
and 50 ms and 80 J/cm
2
and
50 ms were statistically significant for reduced mean
hair counts (p=0.014, p=0.042, respectively), while the
lowest setting at 50 J/cm
2
and 25 ms was not significant
(p=0.079).
In a prospective clinical study with 29 volunteers,
Lorenz et al
42
investigated the efficacy, side effects,
and the long-term results of a long-pulsed Nd:YAG for
hair removal in different hair colors and skin types.
Treatment was performed on the lower leg with a long-
pulsed Nd:YAG. Five test areas were treated one to five
times at monthly intervals; one served as a control.
Follow-up investigations were performed at each ses-
sion, and 3, 6, and 12 months after the last therapy.
The investigators reported after 1 month a hair loss of
greater than 50% in 44.9% of the areas treated once.
With up to five treatments, this percentage increased to
71.5%. One year after therapy, a greater than 50% hair
reduction was still present in 40% of the five-treatment
areas and in 0% of the areas treated only once.
Early published medical papers using Nd:YAG with
carbon lotion reported a 27% to 66% reduction at 3
months after one treatment.
43
In a different study with
long-pulsed Nd:YAG, Goldberg and Samady found that
in 15 subjects (Fitzpatrick skin types I–III) hair reduc-
tion varied between 50% and 60% at 3 months. Laser
energy was delivered through a 1 mm spot size, 30 ms
pulse duration and fluences of 125–130 J/cm
2
for facial
hair and 150 J/cm
2
for non-facial hair. No complica-
tions or adverse effects were reported at any of the
follow-up examinations.
44
Intense pulsed light (550–1200 nm)
This system delivers broad spectrum, non-coherent
radiation with wavelengths of 550–1200 nm. One of
four filters (590 nm, 615 nm, 645 nm or 695 nm) is
used to eliminate shorter wavelengths. In general, filters
with higher cut-off values are used with darker skin
types. Cooling means are recommended (i.e. gel) when
higher energy (30–65 J/cm
2
) light pulses are used.
These properties allow for great variability in selecting
individual treatment parameters and adapting to dif-
ferent skin types and indications. However, because of
the wide spectrum of potential combinations of wave-
lengths, pulse durations, pulse frequency, and fluences,
a great deal of experience is required when using IPL
technology. Proper patient selection and critical diag-
nostics serve to keep the adverse effects of the treatment
to a minimum.
45
Treatment with IPL may be useful for light colored
hair, although more treatment sessions are generally
required. Several studies have demonstrated the long-
term efficacy of the device. In a study of 67 subjects of
Fitzpatrick skin types I–IV, mean hair loss was 48% at 6
months or more after a single treatment. There were no
statistically significant differences in hair count after
single versus multiple treatments.
46
In one study, 60%
hair reduction was reported 12 weeks after a single
treatment with various cut-off filters (34–44 J/cm
2
, two
to five pulses, 1.5–3.5 ms, 20–50 ms delays). Adverse
effects included post-treatment erythema in 7%, hyper-
pigmentation in 3%, and blistering in 11%.
47
In a non-
controlled study of 14 subjects treated with IPL, and
followed for more than 12 months after the last
treatment, a mean of 83% hair reduction was obtained
78
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
after two to six treatments.
48
The authors attributed the
high success rate obtained to the ability of the tech-
nology to provide energy of long wavelengths, selected
high-energy fluences on a specific range and long pulse
durations. However, the results from this study should
be interpreted with caution due to the absence of
controls and lack of uniform treatment and follow-up
control. Side effects and complications of IPL treatment
are similar to those seen after laser-assisted hair removal,
and include rare instances of blistering, crusting, and
transient dyspigmentation.
In summary, the ruby laser (694 nm), alexandrite
laser (755 nm), diode laser (800 nm), intense pulsed
light source (550–1200 nm) and the Nd:YAG laser
(1064 nm), with or without the application of carbon
suspension, work on the principle of selective photo-
thermolysis with the melanin in the hair follicles as the
chromophobe. Regardless of the type of laser used
multiple treatments are necessary to achieve satisfactory
results. After repeated treatments hair clearance of
30–50% is generally reported 6 months after the last
treatment. Patients with dark skin (Fitzpatrick skin
types IV and V) can be treated effectively with com-
parable morbidity to those with lighter skin. Although
there is no obvious advantage of one laser system over
another in terms of treatment outcome (except the
Nd:YAG laser, which is found to be less efficacious, but
more suited to patients with darker skin), laser para-
meters may be important when choosing the ideal laser
for a patient.
49
Essential issues in laser hair
removal
Terminology
Hair removal is an ambiguous term that may carry
different meaning for the patient, the physician and the
industry. ‘Permanent hair removal’ should be distin-
guished from ‘permanent hair reduction’. The former is
defined as the long-term, stable reduction in the number
of hairs regrowing after a treatment regime, which may
include several sessions. The number of hairs regrowing
must be stable over time greater than the duration of
the complete growth cycle of hair follicles, which varies
from 4 to 12 months according to body location.
Permanent hair reduction, on the other hand, does not
necessarily imply the elimination of all hairs in the
treatment area. This means that although laser treat-
ments with these devices will permanently reduce the
total number of hairs, they will not result in a per-
manent removal of all hair. Complete hair loss refers to
a lack of regrowing hairs (i.e. the number of regrowing
hairs is reduced to zero). Complete hair loss may be
either temporary or permanent. Laser treatment usually
produces complete but temporary hair loss for 1–3
months, followed by partial but permanent hair loss.
Temporary growth delay seems to be caused by laser
damage induction of the telogen phase. Permanent hair
loss seems to be associated with miniaturization of hair
follicles.
50
Optimal follicle damage
Which hair cycle phase is the most appropriate, and
which follicular elements cause hair-shaft regeneration
is a subject of debate. In mice, Lin and colleagues noted
that during the anagen phase there was heterogeneous,
but widespread injury to the epithelium, increasing with
increasing fluence (1.47–3.26 J/cm
2
). However, no
follicular damage was observed during the catagen or
telogen phases at any of the fluences used. Full hair
regrowth occurred 28–56 days after laser exposure
administered during the catagen or telogen phases for
all fluence levels. In contrast, regrowth after laser
exposure in the anagen phase was fluence-dependent:
hair regrowth was moderate (1.47 J/cm
2
) and none
(3.16 J/cm
2
).
51
In humans it appears that the most essential variable
is the presence of the pigmented hair shaft within the
skin that functions as a chromophore. It is therefore
likely that both anagen and telogen follicles are sensitive
to laser treatment. Because the telogen bulb is high in
the dermis one might argue that this would be the
optimal time for treatment; however, the superficial
location is undermined by the bulb being poorly
melanized. In early anagen the bulb is well melanized
and still fairly superficial; this may present the best time
for treatment. If the damage is not permanent during
this cycle, follicles move into the telogen stage as they
fall out. Because the duration of the hair cycle differs
for different body sites (Table I), repeat treatments are
usually done when there is a wave of rapid hair
regrowth or between 4 and 8 weeks.
52
Another issue is whether the hair follicle is able to
regenerate from the bulge area if the papilla is destroyed
by a photothermal source. Some researchers claim that
hair follicles can regenerate in the absence of the hair
bulb,
53,54
while others maintain that the destruction of
the hair papilla is essential for permanent epilation.
55
The recent bulge-activation hypothesis maintains that
the bulge area of the outer root sheath near the arrector
pili muscle insertion contains pluripotential cells, which
contribute to the new hair matrix when induced by the
dermal papillae during the late telogen phase.
14
Thus,
injury to the stem cells in the bulge area would lead to
follicular destruction.
Safety and skin color
Although numerous lasers are available for laser-
assisted hair removal, their use in individuals with a
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
79
dark skin type presents many challenges due to com-
petition from epidermal melanin. The ideal candidate for
hair removal is a light-skinned individual with dark
terminal hair. Dark skinned patients with high epider-
mal melanin content are prone to adverse side effects
ranging from immediate pain and pigmentary distur-
bances to scarring. Despite the selection of appropriate
wavelengths and pulse widths of the targeted chromo-
phore, there is light absorption by the overlying epider-
mal melanin (Fitzpatrick skin types IV–VI).
Short wavelength (694, 755 nm) hair removal lasers
can be quite successful in lighter skin types. However,
laser hair removal in Asians can be difficult, and mul-
tiple treatments are usually required for effective treat-
ment. Recently, Hussain et al
56
evaluated the safety and
efficacy of alexandrite laser hair removal in 144 Asian
subjects with Fitzpatrick skin types III–V. The authors
reported that no individuals had scarring or long-term
pigmentary changes and concluded that there does not
appear to be an exact correlation in Asian skin between
complications occurring after test patch treatment and
those seen with subsequent treatments.
In a multicenter prospective study, laser hair removal
was associated with a low incidence of side effects that
were self-limiting in the majority of cases. The highest
incidence of side effects was seen in patients with darker
skin treated with the long-pulsed ruby laser.
57
However,
the parameters for laser hair removal emphasize use for
Caucasians (Fitzpatrick skin types I, II, or III). The
characteristics of oriental skin and hair are black, coarse
hairs in darker skin (Fitzpatrick skin types IV or V) and
therefore the hair is more difficult to remove by laser.
Recently, Lu et al
58
report 146 oriental patients (156
body sites) who underwent treatment with the long-
pulsed alexandrite laser (755 nm wavelength) depila-
tion system. Minimal and transient complications were
noted.
In a retrospect study of 900 patients who underwent
laser-assisted hair removal, Nanni and Alster
59
found
direct association of skin type on the risk of side effects.
Table III describes selected adverse side effects that may
occur during or following laser/light-based hair removal
treatment. Adrian and Shay
60
studied laser hair removal
in African-American patients with skin types V and VI.
Histologic studies examined efficacy and side effects in
an effort to optimize laser hair removal procedures in
this patient population. It was found that both laser
modes could be used safely in skin type V and VI
African-American patients; however, longer pulse dura-
tions enabled the delivery of higher fluences with minor
and acceptable postoperative complication profiles.
In order to avoid thermal damage of the epidermal
matrix, current laser and non-laser devices use various
parameters of cooling means by different techniques.
Currently popular cooling techniques include contact
(circulating cold water at 2–6‡C or sapphire), cryogen
cooling or forced flow of chilled air. In general, the
rational of cooling the skin is to allow the delivery of
higher fluences and short pulse widths into the hair
follicle.
61
During long pulse modes (w100 ms), how-
ever, the epidermis tolerates a narrower temperature
gradient in respect of the cooling method applied. Thus,
to achieve effective epidermal protection, the hair color
(i.e. black, blond), skin type (Fitzpatrick skin types I–VI)
and cooling types should be carefully considered. Since
adverse side effects are directly correlated with skin type,
with darker-skinned and tanned patients experiencing a
much higher rate of complications, skin types IV–VI and
tanned skin are best treated with a diode laser (800 nm)
or a Nd:YAG (1064 nm) laser. A physician who has a
good understanding of hair biology, laser optics, and
patient skin phenotypes is able to improve patient
outcome and reduce untoward adverse side effects.
Nevertheless, no system can provide fully predictable
results.
Treatment frequency
Factors that affect the outcome of treatment include the
hair growth cycle, skin color, hair color and density,
and the quality of the individual hairs. Table IV shows
factors that may influence photoepilation outcome.
Because the duration of the hair cycle differs for dif-
ferent body sites, repeat treatments are usually done. As
a general rule, 6 to 10 laser sessions are required during
the first year to achieve long-term epilation. With most
laser systems, a single treatment can reduce hair by
10–40%; three treatments by 30–70%; and repeated
treatments as much as 90%. These results are main-
tained at post-treatment follow-up for as long as 12
months. Wendy and Geronemus reported a lower level
of hair regrowth after three laser treatments on the face
compared with the back, shoulders and arms.
62
Based
on the duration of cycle length, hairs on the head have
a relatively short telogen phase (6–12 weeks). Thus, a
1-month interval between treatments is a sufficient time
elapse for progression to the anagen phase. On the
trunk, a 2-month interval is more appropriate. Figures 3
Event Occurrence
Dyspigmentation (hyper or hypo) Common
Itching, stinging (during treatment) Common
Pain Atypical
Follicular erythema Common
Epidermal erythema Common
Purpura Uncommon
Crusting/scab formation Uncommon
Swelling Uncommon
Erosions Uncommon
Herpes simplex Uncommon
Scarring Rare
Table III
Adverse side effects during/following photoepilation
80
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
and 4 depict the before (A) and after (B) clinical results
of laser hair removal.
Controversies and limitations
With the proliferation of devices targeting hair and
unsubstantiated claims by manufacturers, significant
confusion exists in this field. Although an ever-
increasing number of published studies have confirmed
the long-term efficacy of laser and light-based treat-
ments, the technology still has limits and risks. Most
studies on laser hair removal are uncontrolled and
have included fewer than 50 patients; none have been
blinded, and all have used a variety of treatment pro-
tocols, equipment, skin types and hair colors. In
addition, none of the presently utilized lasers have
been proven to destroy hair permanently and long-term
results are still lacking. Because lasers and light-based
systems were rushed onto the market without a full
understanding of their capabilities and limitations, it is
vital that researchers, practitioners and consumers
continue to make their experience known to the pub-
lic. Current data on laser and light-based hair removal
are limited by the short duration for which this
technology has been practiced. More long-term studies
with state-of-the-art laser hair removal technology are
still needed to elucidate the optimal parameters clini-
cally appropriate for safe and effective results in all skin
and hair types/colors.
Laser parameters
Wavelength
Fluence
Spot size
Pulse width
Skin cooling system
Skin phenotype
Fitzpatrick skin type I–III
Fitzpatrick skin type IV–VI
Hair characteristics
Hair thickness
Hair color
Follicle depth
Anagen/telogen follicles ratio
Hair anatomical location
Hormonal
Cushing syndrome
Polycystic ovarian disease
Hormonal medications
Testosterone and estradiol
Growth factors (IGF-1)
Others
Gender
Photosensitive medications
Plucking, waxing
Sun tanning
IGF=insulin-like growth factor
Table IV
Factors influencing hair removal efficiency
Figure 4
Clinical results. Skin type III: male. (A) Before
and (B) 3 months after three treatments plus
control. (Courtesy of Pio Donnarumma, MD,
Napoly, Italy.)
Figure 3
Clinical results. Skin type III: female. (A) Before and
(B) 3 months after three treatments. (Courtesy of
Pio Donnarumma, MD, Napoly, Italy.)
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
81
Summary
The use of lasers/light-based technology in the treatment
of unwanted hair has become commonplace in our
society. Today, less than a decade after the first laser hair
removal debut, there are at least 20 manufacturers
producing more than 40 laser/light-based systems.
63,64
The acceptance of photoepilation by both physicians and
patients is a direct reflection of the high degree of efficacy,
low side effects and few complications. The benefits of this
technology, however, have largely been limited to
individuals with dark hair and relatively fair skin.
The major challenge in the field of photoepilation
continues to be the development of technology that not
only permanently and significantly reduces the number
of hairs but also provides permanent and complete hair
removal for all skin and hair types and colors. With
current technology, the average clearance rate is 20–75%
after 1–6 months of follow-up. Long-term studies with a
follow-up of more than 1 year are needed to find out
whether permanent hair removal can be accomplished.
Recently, the increasing public demand for a low-cost
hair removal service has urged new manufacturers to
develop low-priced, compact sized systems, which still
need clinical validation and long-term follow-up.
Photoepilation, although better studied than most
methods and more strictly regulated, has yet to be
proved permanent in all patients and in all hair colors.
With the rapid pace of technological advancements and
continued studies of hair biology, laser physics, skin optics
and cooling means, it is anticipated that permanent hair
removal will be achieved in the near future.
References
1. Olsen EA, Methods of hair removal. J Am Acad Dermatol
(1999) 40: 143–55.
2. Nanni CA, Alster TS, Optimizing treatment parameters
for hair removal using a topical carbon-based solution
and 1064-nm Q-switched neodymium:YAG laser energy.
Arch Dermatol (1997) 133: 1546–9.
3. Goldberg DJ, Unwanted hair: evaluation and treatment
with lasers and light source technology. Adv Dermatol
(1999) 14: 115–40.
4. DiBernando BE, Perez J, Usal H et al, Laser hair removal.
Clin Plast Surg (2000) 27: 199–11.
5. Sun TT, Costsarelis G, Lavker RM, Hair follicular stem
cells: the bulge-activation hypothesis. J Invest Dermatol
(1991) 96: 77S–8S.
6. Abel E, Embryology and anatomy of hair follicle. In:
Olsen EA, ed. Disorders of Hair Growth: Diagnosis and
Treatment. McGraw-Hill: New York, NY, 1994: 1–9.
7. Lin TYD, Manuskiatti W, Dierickx C et al, Hair cycle
affects hair follicle destruction by ruby laser pulses.
J Invest Dermatol (1998) 111: 107–13.
8. Hughes CL, Hirsutism. In: Olsen EA, ed. Disorders of Hair
Growth: Diagnosis and Treatment. McGraw-Hill: New
York, NY, 1994: 337–50.
9. Richards RN, Uy M, Meharg G, Temporary hair removal
in patients with hirsutism: a clinical study. Cutis (1990)
45: 199–202.
10. Kligman A, The human hair cycles. J Invest Dermatol
(1959) 33: 307–16.
11. Ort RJ, Dierickx C, Laser hair removal. Semin Cutan Med
Surg (2002) 21: 129–44.
12. Anderson RR, Parrish JA, Selective photothermolysis:
precise microsurgery by selective absorption of pulsed
radiation. Science (1983) 220: 524–7.
13. Ross EV, Ladin Z, Kreindel M, Dierickx C, Theoretical
considerations in laser hair removal. Dermatol Clin
(1999) 17: 333–55.
14. Rogachefsky AS, Silapunt S, Goldberg DJ, Evaluation
of a new super-long-pulsed 810 nm diode laser for the
removal of unwanted hair: the concept of thermal
damage time. Dermatol Surg (2002) 28:410–14.
15. Fiskerstrand EJ, Svaasand LO, Nelson JS, Hair removal
with long pulsed diode lasers: a comparison between two
systems with different pulse structures. Lasers Surg Med
(2003) 32: 399–404.
16. Altshuler GB, Anderson RR, Manstein D et al, Extended
theory of selective photothermolysis. Lasers Surg Med
(2001) 29: 416–32.
17. Anderson RR, Parrish JA, The optics of human skin.
J Invest Dermatol (1981) 77: 13–19.
18. Anderson RR, Laser–tissue interactions. In: Goldman
MP, Fitzpatrick RE, eds. Cutaneous Laser Surgery: The Art
and Science of Selective Photo-thermolysis. Mosby-Year
Book: St Louis, 1994: 1–18.
19. Lou WW, Quintana AT, Geronemus RG, Grossman MC,
Prospective study of hair reduction by diode laser
(800 nm) with long-term follow-up. Dermatol Surg
(2000) 26: 428–32.
20. Nestor MS, Laser hair removal: clinical results and
practical applications of selective photothermolysis. Skin
Aging (1998) 10: 34–9.
21. Lask G, Elman M, Slatkine M, Laser-assisted hair removalby
selective photothermolysis. Preliminary results. Dermatol
Surg (1997) 23:737–9.
22. Lask G, Eckhouse S, Slatkin M et al, The role of laser and
intense light source in photoepilation: a comparative
evaluation. J Cutan Laser Ther (1999) 1: 3–13.
23. Dierickx C, Hair removal by lasers and intense pulsed
light sources. Dermatol Clin (2002) 20: 135–46.
24. Allison KP, Kiernan MN, Waters RA, Clement RM,
Evaluation of the ruby 694 Chromos for hair removal in
various skin sites. Lasers Med Sci (2003) 18: 165–70.
25. Campos VB, Dierickx CC, Farinelli WA et al, Ruby laser
hair removal: evaluation of long term efficacy and side
effects. Lasers Surg Med (2000) 26: 177–85.
26. Polderman MC, Pavel S, le Cessie S et al, Efficacy,
tolerability, and safety of a long-pulsed ruby laser system
in the removal of unwanted hair. Dermatol Surg (2000)
26: 240–3.
27. Grossman MC, Dierickx C, Farinelli W et al, Damage to
hair follicles by normal-mode ruby laser pulses. JAm
Acad Dermatol (1996) 35: 889–94.
28. Chana JS, Grobbelaar AO, The long-term results of ruby
laser depilation in a consecutive series of 346 patients.
Plast Reconstr Surg (2002) 110: 254–60.
82
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
29. Gault DT, Grobbelaar AO, Grover R et al, The removal of
unwanted hair using a ruby laser. Br J Plast Surg (1999)
52: 173–7.
30. Wimmershoff MB, Scherer K, Lorenz S et al, Hair
removal using a 5-msec long pulsed ruby laser. Dermatol
Surg (2000) 26: 205–9.
31. McDaniel DH, Lord J, Ash K et al, Laser hair removal: a
review and report on the use of the long-pulsed
alexandrite laser for hair reduction of the upper lip,
leg, back, and bikini region. Dermatol Surg (1999) 25:
425–30.
32. Laughlin SA, Dudley DK, Long-term hair removal using
a 3-millisecond alexandrite laser. J Cutan Med Surg
(2000) 4: 83–8.
33. Lloyd JR, Mirkov M, Long-term evaluation of the long-
pulsed alexandrite laser for the removal of bikini hair at
shortened treatment intervals. Dermatol Surg (2000) 26:
633–7.
34. Garcia C, Alamoudi H, Nakib M, Zimmo S, Alexandrite
laser hair removal is safe for Fitzpatrick skin types IV–VI.
Dermatol Surg (2000) 26: 130–4.
35. Ort RJ, Dierickx C, Laser hair removal. Semin Cutan Med
Surg (2002) 21: 129–44.
36. Sanchez LA, Perez M, Azziz R, Laser hair reduction in
the hirsute patient: a critical assessment. Hum Reprod
Update (2002) 8: 169–81.
37. Dierickx CC, Grossman MC, Farinelli WA, Hair removal
by a pulsed, infrared diode laser system. Lasers Surg Med
(1998) 10 (suppl): 198.
38. Campos VB, Effect of pretreatment on the incidence of
side effects following laser hair removal with long pulsed
diode laser in skin types III and IV. Lasers Surg Med
(2000) 26: 177–85.
39. Lou WW, Quintana AT, Geronemus RG, Grossman MC,
Prospective study of hair reduction by diode laser
(800 nm) with long term follow-up. Dermatol Surg
(2000) 26: 428–32.
40. Sadick NS, Prieto VG, The use of a new diode laser for
hair removal. Dermatol Surg (2003) 29: 30–4.
41. Rogachefsky AS, Becker K, Weiss G, Goldberg DJ,
Evaluation of a long-pulsed Nd:YAG laser at different
parameters: an analysis of both fluence and pulse duration.
Dermatol Surg (2002) 28: 932–5; discussion 936.
42. Lorenz S, Brunnberg S, Landthaler M, Hohenleutner U,
Hair removal with the long pulsed Nd:YAG laser: a
prospective study with one year follow-up. Lasers Surg
Med (2002) 30: 127–34.
43. Goldberg DJ, Littler CM, Wheeland RG, Topical suspen-
sion-assisted Q-switched Nd:YAG laser hair removal.
Dermatol Surg (1997) 23: 741–5.
44. Goldberg DJ, Samady JA, Evaluation of a long-pulse Q-
switched Nd:YAG laser for hair removal. Dermatol Surg
(2000) 26: 109–13.
45. Raulin C, Greve B, Grema H, IPL technology: a review.
Lasers Surg Med (2003) 32: 78–87.
46. Gold MH, Bell MW, Foster TD et al, Long-term epilation
using the EpiLight broad band, intense pulsed light hair
removal system. Dermatol Surg (1997) 23: 909–13.
47. Weiss RA, Weiss MA, Marwaha S, Harrington AC, Hair
removal with a non-coherent filtered flashlamp intense
pulsed light source. Lasers Surg Med (1999) 24: 128–32.
48. Sadick NS, Weiss RA, Shea CR et al, Long-term
photoepilation using a broad-spectrum intense pulsed
light source. Arch Dermatol (2000) 136: 1336–40.
49. Liew SH, Laser hair removal: guidelines for manage-
ment. Am J Clin Dermatol (2002) 3: 107–15.
50. SDRH Consumer Information. http://www.fda.gov/cdrh/
consumer/laserfacts.html
51. Lin TY, Manuskiatti W, Dierickx CC et al, Hair growth
cycle affects hair follicle destruction by ruby laser pulses.
J Invest Dermatol (1998) 111: 107–13.
52. Dierickx CC, Campos VB, Lin D et al, Influence of hair
growth cycle on efficacy of laser hair removal. Lasers
Surg Med (1999) 11 (suppl): 21.
53. Oliver RF, The experimental induction of whisker
growth in the hooded rat by implantation of dermal
papillae. J Embryol Exp Morph (1967) 18: 46–51.
54. Cotsarelis G, Sun TT, Lavker RM, Label-retaining cells
reside in the bulge area of pilosebaceous unit: implica-
tions for follicular stem cells, hair cycle, and skin
carcinogenesis. Cell (1990) 61: 1329–37.
55. Holecek BU, Ackerman AB, Bulge-activation hypothesis
is it valid? Am J Dermatol (1993) 15: 235–57.
56. Hussain M, Polnikorn N, Goldberg DJ, Laser-assisted hair
removal in Asian skin: efficacy, complications, and the
effect of single versus multiple treatments. Dermatol Surg
(2003) 29: 249–54.
57. Lanigan SW, Incidence of side effects after laser hair
removal. J Am Acad Dermatol (2003) 49: 882–6.
58. Lu SY, Lee CC, Wu YY, Hair removal by long-pulse
alexandrite laser in oriental patients. Ann Plast Surg
(2001) 47: 404–11.
59. Nanni CA, Alster TS, Laser assisted hairremoval: side effects
of Q-switched Nd:YAG, long-pulsed ruby, and alexandrite
lasers. J Am Acad Dermatol (1999) 41: 165–71.
60. Adrian RM, Shay KP, 800 nanometer diode laser hair
removal in African American patients: a clinical and
histologic study. J Cutan Laser Ther (2000) 2: 183–90.
61. Nelson JS, Majaron B, Kelly KM, Active skin cooling in
conjunction with laser dermatologic surgery. Semin
Cutan Med Surg (2000) 19: 253–66.
62. Lou WW, Geronemus RG, Dermatologic laser surgery.
Semin Cutan Med Surg (2002) 21: 107–28.
63. Moretti M, The worldwide epilation market. Medical
Insight Inc. www.miinews.com, Version 2, December 2001.
64. Waldorf HA, Optimizing laser hair removal. Cosmetic
Dermatol (2002) 15: 53–7.
J Lepselter and M Elman Biological and clinical aspects in laser hair removal
83