By Tajmirriahi ,Nabet
In the supervision of Dr. Asilian ,Ali MD
(1) The damage may result from
direct photothermal
destruction, whereby a light source emitting a wavelength in the
desired chromophore
melanin (600–1100 nm) results in selective heating of the hair
shaft, follicular epithelium, and hair matrix. However, the pulse
duration theoretically should be equal to or shorter than the thermal
absorption spectrum of the
relaxation time of the hair follicle (10–100
msec depending on the
size) in order to maintain spatial confinement of the thermal damage. A
cooling device may be used to limit thermal damage to the
epidermis containing competing melanin chromophore, by means
of a cooled glass chamber, cooled sapphire window, a cooled gel layer, or a
pulsed cryogen spray. Available photothermal destruction methods include the
normal-mode 694 nm ruby, normal-mode 755 nm alexandrite, 800–810 nm
pulsed diode, long-pulsed Nd:YAG lasers, and filtered flashlamp technology.
(2) Photomechanical destruction method relies on the damage induced by
the photoacoustic shock waves generated when very
short pulsed
light source causes rapid heating of the melanin
chromophore within the hair follicle, inducing
trauma to the surrounding bulbar melanocytes without follicular
disruption.
Q-switched Nd:YAG laser and carbon suspension Q-switched
Nd:YAG laser employ this method.
photosensitizer is
used in conjunction with a light source. In photodynamic
therapy, aminolevulinic acid (ALA) becomes rapidly converted to
protoporphyrin IX (PPIX) by epithelia cells. A photodynamic reaction
occurs when a photon-activated PPIX reacts with molecular oxygen to
(3) Photochemical destruction results when a
form singlet oxygen species that result in oxidative cell damage.
Anagen follicles of terminal hair extend deeply into the subcutaneous fat, lying 2–7
mm below the skin surface.
However, sometimes the actual target
is not pigmented and is at
some distance from a pigmented structure. For example, the
follicular
stem cells, which line the outer root sheath, are not
pigmented and are at some distance from the
pigmented hair shaft.
These cells appear to be an important target for permanent hair destruction. The
concept of thermal damage time (TDT) has therefore been
proposed in the case of the hair follicle. Pulses longer than the thermal relaxation
time of the hair shaft allow propagation of the thermal damage front through the
.(.100 msappears .entire volume and better damage of the follicular stem cells.
The bulb of a telogen, or club, hair is unpigmented because of the cessation of
melanin production during the catagen stage. In fact, the cessationof
melanin production is the first sign of catagen. As
anagen progresses, the bulb and papilla descend deeply
into the dermis so that late anagen hairs may also be somewhat laser
resistant to treatment. It would seem, therefore, that it is in early
anagen that hair follicles are most sensitive to laser
induced injury. Since any injury, even a laser injury,
may induce telogen, the timing of a second laser
treatment after the first laser induced telogen formation, becomes critical.
As the laser resistant terminal
follicles now enter an
anagen growth phase, after a first treatment, the second treatment
may be more effective than the first. Conversely, a second
treatment given too early, or too late, would be expected to have
little effect.
Lin et al postulate that follicles treated in the telogen phase show only a
growth delay for weeks, whereas, when those follicles are treated in the
anagen phase they may be susceptible to lethal damage, may have a growth delay,
or may simply switch into telogen phase. This could partly explain the growth
dynamics of the hair cycle. Repeated treatments could lead to a
synchronization of the anagen phase by induction and/or shortening of
the telogen phase,which could increase the effiveness of hair removal with
each consecutive treatment. Another explanation might be that the follicle is
not destroyed immediately, but shows a growth arrest after only one
(shortened) anagen cycle. Some have questioned the assumption that effective
laser hair removal is determined solely by treating hairs in the anagen cycle.
These investigators suggest that melanin within a hair follicle may
be more important than the actual time of treatment.
Based on our current understanding of hair biology, knowledge of the hair cycle
and especially the length of telogen, becomes essential for determining whether
laser or light source treatment of unwanted hair is ‘temporary’ or ‘permanent’.
Currently, there is no agreement on a definition for treatment induced permanent hair
loss Permanence, defined as an absolute lack of hair in a treated area for
the lifetime of the patient, may be an unrealistic goal. Dierickx et al. have
suggested a more practical approach. They defined ‘permanent’ hair loss as a
significant reduction in the number of terminal hairs, after a given
treatment, that is stable for a period longer than the complete growth
cycle of hair follicles at any given body site.
Telogen may last 3–7 months on the thighs and chest. After telogen, the follicle will .
then recycle into anagen. This will also last 3–7 months. Thus hair may be considere
permanently removed from these locations if there is no recurrence after this
complete time period. Olsen has suggested an even longer time period. She suggests
that permanent hair reduction would be deemed to have occurred after the lapse of
6 months after complete growth cycle. If no hair regrows after this time period, it
can be assumed that the growth centers have no capacity to recover from injury.
Permanent hair reduction is defined by the FDA as stable decrease in the
number of terminal hairs for a period longer than the complete
hair cycle at a given site following a treatment regime, which may include
multiple sessions.
1.Laser induces catagen phase
2.One of the uncertainties in laser hair removal is the exact tissue target.
Although not definitively proven, from the above discussion of the hair cycle
and follicular stem cells, it appears that complete destruction of hair follicle
without regeneration potential may occur when both the germinative cells in
the bulb and the stem cells in the bulge area are destroyed. As follicular stem
cells appear to be very resilient to thermal damage, this may be diffi cult
to achieve
It should be noted that there is a general consensus that hair removal results
will always be affected by chosen anatomic site. Most investigators note a
better response on chest, face, legs, and axilla.
Lesser responses appear to occur on the back, upper lip, and
scalp. In addition, terminal hairs, and not vellus hairs respond
to laser treatment.
The
ideal patient has realistic expectations, normal
endocrine status, with thick dark hair and light skin tones .
There are differences in the anagen:telogen ratio depending on the area that is
treated. For example the axillae and bikini areas have a higher anagen:
telogen ratio than the legs, arms, and chest. Therefore, it has been suggested
that these areas would respond better to laser hair removal with more noticeable
in hair density.difference
It is now widely accepted that almost any laser can induce temporary hair loss.
Fluences as low as 5 J/cm 2 can induce this effect. The effect tends to last 1–3
months.
The mechanism of action appears to be an
induction of
catagen and telogen.
Permanent hair reduction, occurring at higher fluences is seen in
80% of individuals and is fluence dependent. Thus, the greater the
delivered fluence, all else being equal, the better are the
expected results.
Dark
hair with ample amounts of eumelanin can be effectively treated
by multiple devices, provided that appropriate fluence and spot size are used.
Under these conditions, the average long term hair loss per treatment is
about 20-30% based on studies performed with ruby lasers.
Multiple treatment sessions are usually required to achieve the
maximal level of hair reduction.
blonde, red, gray, or white hair
In individuals with
, it
is unlikely that laser treatment will produce the same degree of longlasting hair
removal. However, such patients may be willing to undergo treatments
spaced about 2-4 months apart as necessary to
maintain temporary hair loss.
While treatment can be safely performed with a shorter
wavelength device (e.g. ruby laser) in fair skinned
patients, it is preferable to use longer wavelength devices in
darker skinned patients.
The first laser hair removal system employed was the normalmode ruby laser, but the pulse duration of 0.3 ms was not efficacious
longer pulse durations of 0.7-0.8 ms
subsequently
increased its usefulness. When the pulse duration of the ruby laser
was lengthened to 3 ms, permanent hair removal was demonstrated
however, there was a significant risk of
dyspigmentation.
In general, use of the ruby laser for hair removal
patients with skin types I-III, since absorption of
is limited to
694 nm light by epidermal melanin
results in a higher risk of complications (e.g. blistering, pigmentary changes) in individuals with darkly
pigmented skin.
However, sometimes the actual target
is not pigmented and is at
some distance from a pigmented structure. For example, the
follicular
stem cells, which line the outer root sheath, are not
pigmented and are at some distance from the
pigmented hair shaft.
These cells appear to be an important target for permanent hair destruction. The
concept of thermal damage time (TDT) has therefore been
proposed in the case of the hair follicle. Pulses longer than the thermal relaxation
time of the hair shaft allow propagation of the thermal damage front through the
.(.100 msappears .entire volume and better damage of the follicular stem cells.
BOLOGNIA:
Multiple studies have demonstrated effective hair removal with the
long-pulsed alexandrite laser at fluences of 10-40 J/cm2 and
pulse durations of 2-20 ms. At fluences of 20-40 Jlcm2, several
investigators have reported hair reductions of 70-80% after multiple (at
least 3-5) treatments. Use of the long-pulsed alexandrite in patients
with darkly pigmented skin has been reported, but side effects such as
blistering and pigmentary alteration can occure in general, this laser is
best suited for hair removal in patients with skin types I-III.
Red hair
contains pheomelanin, which absorbs poorly at any wave-length,
but especially beyond 800 nm. Therefore, shorter wave-lengths, such as those of
ruby or alexandrite lasers are needed in these patients.
In cases of low contrast between skin tone and hair color,
such as darkly pigmented individuals or light hair in fair individuals, a
significant portion of emitted light is absorbed by the epidermal
melanin. This occurs because epidermal melanin absorbs energy not only from
direct exposure, but also from backscattering. As
wavelengths of light increase, a greater ratio of dermalto-epidermal deposition of energy results in greater safety in
such individuals.
Depending on the semiconductor used in the system, diode
lasers can vary widely in their emitted wavelengths. Those
manufactured using derivatives of gallium arsenide produce wavelengths
between 660 and 900 nm, whereas those utilizing indium
phosphide emit light with wavelengths between 1300 and 1550 nm.
hair removal
produce 800- or 810-nm light.
Diode lasers currently used for
Both 800 and 810 nm wavelengths are absorbed by melanin to a slightly
lesser degree compared to the alexandrite laser.
Absorption is also approximately 30% less than that of the 694 nm
Decreased absorption by
epidermal melanin permits safe
treatment in patients with skin types I to
IV .
wavelength.
Although the rates of melanin absorption by diod laser is lower than the ruby and
alexandrate, the
rates of hair reduction with the diode laser
are similar to those observed with the alexandrite laser,
likely due to deeper penetration into the dermis . Treatment with the
diode laser can be somewhat
to greater
more painful,
however, at least partly due
volumetric heating of tissue. If necessary, pain
can be partially alleviated by reducing the frequency of
delivered pulses.
undergoing
isotretinoin therapy without increase in adverse effect
or longterm sequela,the isotretinoin use should be
avoided in general up to 6 month beforehair removal.
A diode laser was safely used in several patients
Although significantly less well absorbed by melanin compared to
previously described wavelengths, light at 1064 nm is able to
penetrate deep into the dermis, up to 4 to 6 mm. Originally used
in Qswitched mode with or without topical application of carbon particle suspension,
the new millisecond systems appear to offer good results especially for
darker skin types, albeit at a price of slightly
decreased
efficacy in lighter skin
Although comparable in
lighter skin types (I to III), the
incidence of complications in skin types IV to VI is considerably
lower with the long-pulsed Nd:YAG than with the other lasers.
Hair removal using Nd:YAG laser has been found to be considerably more
painful than that with diode lasers, likely due to even greater
heating with the former
volumetric
For persons with very dark skin and blonde or gray hair, an effective
permanent laser hair removal treatment is still lacking. Potentially, the
exogenous chromophore approach could solve this problem. Rather than
targeting endogenous melanin, an exogenous chromophore (like dyes,
photosensitizers, or carbon particles) can be introduced into the hair follicle
and then irradiated with light of a wavelength that matches its absorption peak.
The main problem is reliable penetration of the chromophore into all depths of the
hair follicle.
Therefore, the technique, in its present form, is apparently inadequate for inducing
permanent hair loss. However, in vitro testing has recently shown that a new
method could increase the quantity and the penetration depth of dyes in
follicular ducts.
Q-switched Nd:YAG lasers have been used to target topically applied carbon
particles that have previously been applied to the hair follicle.
This method was one of the first available laser hair removal techniques. This
short term hair removal technique has also been used without the prior application of
carbon.
Immediately after Q-switched 1064-nm laser irradiation of carbon coated hairs,
the car bon is heated to its vaporization temperature of about 3,700 °C. Vaporization
leads to a huge volume expansion with resultant supersonic proliferation of high
pressure waves. These shock waves, in turn, produce mechanical damage, as
well as the development of heat. It is not clear how much mechanical and/or heat
energy produced by this mechanism is required for destruction of a hair
follicle. However, histologic evidence of follicular damage is seen after such a laser
exposure. This results in a clinical delay of hair growth.
purpura, up to 18%, have previously been reported
treatment with Q-switched Nd:YAG lasers , this does not
Although high rates of
following
appear to occur with the long-pulsed
lasers.
Laser treatments for hair removal are generally well tolerated by
patients and do not usually require anesthesia. However, because
anesthesia is
necessary when treating large surfaces of the body
or sensitive areas such as the upper lip and bikini
area. Local infiltration of anesthetic or nerve blocks using 2% lidocaine
the hair follicle is surrounded by nerve endings, topical
can also be useful in selected patients.
Pulses are delivered in a slightly overlapping mode with a predetermined spot
size. The ideal immediate response is vaporization of the hair shaft, followed
erythema a few minutes later by the appearance of perifollicular edema and
It is generally recommended that the highest tolerable fluence and the
largest spot size be used in order to obtain the best results. However,
excessive fluences that cause epidermal separation or blistering should
If the device is not equipped with a cooling
mechanism, a thick layer of cool gel is applied before the
be avoided.
delivery of laser pulses.
Epidermal cooling during treatment accomplishes two goals.
First, it minimizes the risk of epidermal damage due to
absorption by epidermal melanin. Such damage may result in blistering,
discoloration, and scarring, and is especially important for darker
pigmented individuals. Therefore, epidermal cooling allows for use of higher fl
uences while minimizing the risk of epidermal damage.
temporary anesthetic effect,
Second, it has
thus reducing patient discomfort
during treatment. Epidermal cooling can be separated into contact and noncontact. Contact cooling may include cold gel, chilled sapphire window, and
cooled copper plate. Non-contact cooling includes cold air convection and
dynamic cooling with automatic spraying of liquid cryogen, tetrafl uoroethane,
immediately prior to laser pulse.
After being scattered, photons closer to the center of the beam may, in
fact, regain the initial direction of travel through their interaction with
other photons. On the other hand, if scattered, photons at the periphery of
laser beam may not be able to regain it. Therefore, the percentage of
light lost to scattering is larger for smaller beam
diameter, or spot size, than for a larger one. Two corollaries of this principle are
that energy density, or fl uence, is lowered for larger spot sizes and that a very
small spot size may, in fact, not allow for suffi cient depth of penetration, even with
longer wavelengths. Thus, the largest spot size accommodated by the size of the
treatment area may lead to better effi cacy, as well as decreased overall treatment
time.
the choice of fl uence depends of
the amount of chromophore in the target structure, as
well as selected wavelength. Higher fl uences are
needed when the amount of chromophore is reduced, as
After a spot size is selected,
represented by blonde or thinner-caliber hair. As well, as
was previously discussed, higher fl uences are used with longer wavelengths
due to the nearly linearly decreasing absorption of light by melanin at those
wavelengths. In addition, fl uences diminish rapidly as a function of the depth of
penetration, as progressive absorption and scattering result in decay of the original
energy. Therefore, even though temporary hair removal will occur at almost any fl
higher fluences may result in longerlasting or more permanent hair reduction.
uence,
For all laser and light systems, the immediate treatment
endpoint is
vaporization of the hair shaft. This is followed in a few seconds
to minutes by mild erythema and perifollicular edema.
In general, these should resolve within 10 to 60 minutes. More
widespread erythema or confl uent edema may indicate epidermal
and dermal damage, respectively. If noted, lower fl uence, longer pulse
duration, or better cooling should be utilized.
Gray or white discoloration immediately following laser pulse and
lasting a few seconds is an indication of epidermal damage and
should be avoided.
During treatment,
pressure
may be applied to the skin
before
each pulse. This maneuver leads to decreased depth of the bulb and the
bulge, increased penetration of light into the dermis, and
decreased amount of hemoglobin,
a competing
chromophore, in dermal capillaries. Recently, a pneumatic
skin
flattening device using negative pressure was introduced in conjunction
with lasers and IPL devices. This technique may reduce intra-operative
pain and post-treatment erythema and edema, while
similar or enhanced efficacy compared to .providing more uniform cooling and
conventional photoepilation.
Research has shown that laser hair removal requires the presence of a
pigmented hair shaft. Retreatment can therefore be performed as soon
as regrowth appears.
Regrowth is based on the natural cycle, which varies by anatomic location ,
but on average, the timing is 6–8 weeks. More research regarding
this is currently being conducted.
Repeated
treatments may synchronize the anagen phase by induction
and/or shortening of the telogen phase which could lead to increased
effectiveness of hair removal at each consecutive treatment. Alternatively, the
follicle may show growth arrest after one shortened anagen cycle
Temporary hair loss (1–3 months) always occurs after laser treatment,
regardless of hair color or device used. On the other hand, the ability to induce longlasting hair reduction is strongly correlated with hair color. Patients
dark hair
with
are most likely to obtain longlasting hair removal. Blonde-,
red-, gray-, or white-haired patients are unlikely to experience a permanent
reduction, because melanin is low or lacking in the hair follicles.