| LASERS AND LIGHTS | ARTICLE 1000 100
Melanin Oxyhaemoglobin
10 Through study, the principle
chromophore for the removal of unwanted hair is the pigment in the hair itself; thus melanin is the principle chromophore that devices designed for hair removal must focus on.
1
n Delivering sufficient energy, defined by the fluence given, to heat the associated chromophore and destroy the target. In addition, the use of appropriate spot sizes is
0.1 500 600 700 800 Wavelength (nm) of unwanted hair adhere to the principle of selective
photothermolysis, described by Anderson and Parrish in 19833
. The principle of selective photothermolysis states
that through the use of one of these myriad devices, a thermal injury can be confined to a specific chromophore within the skin and within a target (i.e. a hair follicle), and that with this selective energy disruption, all other targets in the area of the specified target are virtually left untouched or without collateral damage. Through study, the principle chromophore for the
removal of unwanted hair is the pigment in the hair itself; thus melanin is the principle chromophore that devices designed for hair removal must focus on. Melanin has been determined as present in the hair shaft, in the outer root sheath of the infundibulum, and in the matrix area of the hair bulb. Early systems for laser hair removal targeted the melanin in the hair follicle, and were effective when used to treat dark hairs (with the most melanin) on light-skinned individuals. Darker-skinned individuals treated with some of these early machines had too much competition for melanin, and
therefore caused adverse events and
post-inflammatory hyperpigmentation (PIH). In addition, Adrian4
noted the existence of a vascular
component in laser hair removal, providing a second chromophore for those treating patients with some of the early devices. The author has used this process and the associated chromophore injury pattern for many years, creating a vascular response in some patients for effective hair removal5
melanin and haemoglobin are shown in Figure 1. Once a chromophore has been established, then it is
imperative to have other necessary ingredients for the principle of selective photothermolysis to be successful: n Choosing a wavelength of light that adheres to the chromophore
n Delivering the energy within a specific time-frame or pulse duration, to ensure that the tissues can respond to the light and not be over its own thermal relaxation time to avoid an increase in adverse events
prime-journal.com | March 2012
Figure 1 Absorption curve of haemoglobin and melanin
900 1000
important to ensure an accurate depth of impact with laser hair removal devices. Accurate epidermal cooling is also essential, and has revolutionised therapies by allowing the physician to bypass the epidermis in many instances, allowing more skin types to be effectively treated with appropriate cooling6
. As noted, a variety of lasers and light sources are
Figure 2 Energy penetration of commonly used cutaneous lasers, wavelengths and depths
available for the treatment of unwanted hair. What has become evident in laser hair removal is that those systems with longer wavelengths appear to be the those that garner the most attention in laser circles. For the most part, the ruby laser, the first system described in the literature, has virtually disappeared from practical use and has become a footnote in the laser hair removal annals. However, as the world is becoming ÔdarkerÕ, more skin of colour patients are presenting to clinics for laser hair removal, and it has been shown that longer wavelength laser systems penetrate deeper and are more effective in this patient group by effectively targeting the entire hair bulb (Figure 2). Many physicians in laser hair removal mention tanned skin. The diode laser, for instance, has Food and Drug Administration (FDA) clearance for use on tanned skin. However, the author strongly contends that no one
. The absorption spectrum of both
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Absorption/Scattering coefficient (1/cm)
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