Despite its limitations, electrolysis for many years was the most popular method of longterm or permanent hair removal. The introduction of laser-based hair removal procedures in the 1990s has now replaced most of the electrolysis market. This method of hair removal is based on the concept developed by Anderson and Parrish in 1983, commonly known as ‘selective photothermolysis’ [63]. The principle behind this concept is preferential absorption of certain wavelengths of light by the hair follicle chromophore melanin, resulting in a significant damage to the hair-fiber producing structures with minimal effect on the surrounding tissues [64]. Melanin in hair follicles is produced by, and is concentrated in melanocytes which are present in the vicinity of the hair matrix and dermal papilla cells that regulate hair growth and cycling. By causing significant thermal damage to these cell types, the hair-growth processes can be interrupted or permanently halted, depending on the extent of damage caused. It is proposed that in order to achieve permanent hair removal, it may be necessary to also damage the stem cell population located in the ‘bulge’ region [65-67].
There are two types of light sources that are used for photo-epilation procedures: laser and intense pulsed light (IPL). Both operate in the red or near-infrared wavelength region of the light spectrum, the principle difference being that the laser sources have a coherent beam of a single wavelength of light, whereas the IPL devices are based on a slice of light spectrum, typically between 590-1200 nm, and the beam is noncoherent. The near infrared wavelengths allow for selective absorption by the hair follicle melanin and combined with deep dermal penetration and careful selection of the pulse durations, the thermal damage can be confined to the hair follicle. There are four major types of hair removal lasers defined by the wavelength they produce: Ruby (694 nm) [67,68], Alexandrite (755 nm) [69], Diode (about 810 nm) [70], and Nd:YAG (1064 nm) [71]. In general, the Ruby laser is most suited for treatments of light skin and dark hair, whereas, Nd:YAG is mostly used for darker skin tones. An optimum combination of laser/light source, wavelength, pulse duration, fluence (energy), and epidermal cooling is selected to effect hair growth on an individual, based on the person’s skin and hair color and the site of treatment [72-77]. Effective permanent hair reduction can be achieved without significant dermal adverse effects [67]. However, aggressive use of laser to achieve higher efficacy or using inappropriate laser parameters especially on darker skin tones, can result in significant skin effects ranging from edema, crusting, burning, scarring, to longer-lasting pigmentary changes [78,79]. Laser hair removal is described in detail in later chapters of this book.