Biomedical Engineering Reference
In-Depth Information
In our experience, when treating subjects with dark skin, the
ruby laser system is associated with higher risk of adverse
effects, especially transient hyper- and hypopigmentation.
This results from the melanin interface of the 694-nm light
pulse of the ruby lasers. However, the alexandrite, diode, and
LP 1064-nm Nd:YAG lasers; and the IPL source operating at
longer wavelength and longer pulse widths have been used to
treat these patients safely when combined with cooling devices.
Permanent pigmentary alterations (Fig. 13.24) and scarring
were rare except in cases of overaggressive treatment or post-
operative infection.
A retrospective study of the side effects of laser-assisted hair
removal treatment in skin phototypes I-V found that the QS
Nd:YAG laser resulted in the fewest side effects, whereas the LP
ruby and the LP alexandrite lasers produced equivalent adverse
effects but greater effi cacy than that of QS 1064-nm Nd:YAG
laser (249). Long-term adverse sequelae and scarring were not
observed with any of the laser systems under study. Although
it caused the fewest side effects, the 1064-nm QS Nd:YAG sys-
tem does not typically produce long-term hair reduction
because of its very low absorption by melanin and the use of
low treatment energy fl uences (255).
As anticipated, lasers with longer wavelengths produce fewer
adverse effects. A hair removal study comparing the effi cacy
and complications of diode and LP 1064-nm Nd:YAG lasers in
Chinese patients with skin phototypes IV or V noted no pig-
mentary or textural changes after treatment, even in skin pho-
totype V patients (231). However, the disadvantage of the LP
Nd:YAG hair removal system is that the absorption of this
laser light by melanin is decreased compared with that of the
ruby laser, such that absorption by the completing chromo-
phore, oxyhemoglobin, is substantially increased.
Pulse duration of hair removal light sources is the second
important parameter for effective hair removal without epi-
dermal injury (256). A pulse duration of approximately
10-50 ms will damage hair follicles with less epidermal injury.
However, caution should be exercised when using very long
pulse widths to treat dense hair areas because of thermal con-
duction between closely adjacent hair follicles.
The last important factor to be considered is epidermal
cooling. Integrating surface cooling into the delivery confi gu-
ration is one way to protect the epidermis and consequently
prevent or minimize the adverse sequelae of the procedure.
Presently, fi ve types of cooling are used in conjunction with
lasers and IPL systems: (
i
) passive cooling with a chilled aque-
ous gel; (
ii
) active cooling with water encased in a glass hous-
ing; (
iii
) active conductive cooling with water encased in a
sapphire window; (
iv
) dynamic active cooling with a cryogenic
spray; and (
v
) air cooling with a refrigerated air stream. These
cooling confi gurations can provide epidermal preservation
compared with no surface cooling (242,246).
Paradoxical hypertrichosis is a rare but signifi cant side effect
of photoepilation that has received more attention in the lit-
erature (257-259). Initially reported with IPL therapy (260),
this adverse effect has now been seen after long-pulse alexan-
drite (257) and diode laser (261) treatment and is likely to be
common to all current laser and light hair removal devices
(258,259,262). The most common location of terminal hair
growth, which has been noted in several studies, is on the
lower face in women although reports on the backs of men
have also been described. The majority of patients developing
hair induction had dark skin types (III or IV).
The etiology of this “paradoxical effect” of increased hair
growth in response to laser and light photoepilation remains
unclear but some have speculated that it is lower-range fl u-
ences of laser and light in individuals with darker skin types,
which paradoxically stimulates hair growth. Therapy for par-
adoxical hypertrichosis is based on two facets: treatment of
the already present induced hair and the prevention of hair
induction. Several researchers suggest the continuation of
treatments by using higher fl uences and inclusion of the new
hairy areas in the treatment areas, because induced hair
responds to treatment in the same manner as other hair
follicles.
In conclusion, in Asian patients, laser- and pulsed light hair
removal systems provide comparable clinical effi cacy to that of
white-skinned patients. Treatment parameters must be indi-
vidualized for each patient and with each device. When per-
forming this procedure in darker skin individuals, a range of
test fl uences should be performed in an inconspicuous area
prior to performing complete treatment. A delay of at least
1 hour should elapse prior to evaluation of test spots. In our
practice, darker skin tones can be safely and effectively treated
using a light source with a longer wavelength than that of a
ruby laser (>694 nm) with a pulse duration of 10-50 ms and
an adequate cooling device. Although laser hair removal treat-
ments are generally effective, clinical challenges still exist. An
optimal fl uence setting needs to be found that is not low
enough to stimulate hair growth and not high enough to cause
burning, erythema, and other unwanted side effects.
prevention and management
of complications
Various attempts have been made to reduce the occurrence of
side effects of laser treatment in Asian skin. These include sun
avoidance, the use of preoperative and postoperative treat-
ment regimens and proper techniques for epidermal cooling.
Figure 13.24
A 24-year-old Thai woman with skin phototype IV developed
persistent postinfl ammatory hypopigmentation 8 months after one treatment
with an 800-nm diode laser hair removal with a sapphire contact-cooling tip
using a fl uence of 30 J/cm
2
with a 30-ms pulse duration.
