Removal of Hair by Light Sources

The introduction of various light sources for hair removal is a result of the growing demand for a rapid, noninvasive method for hair removal. Light source of hair removal commonly focuses on ruby, alexandrite, diode, and Nd:YAG lasers and intense pulsed light sources. These devices are designed to target either an endogenous chromophore (melanin) or an exogenous chromophore (carbon suspension, photosensitizer, and exogenous dye). Laser hair removal is one of the most recent systems of hair removal to be introduced. Today, a large number of specific laser systems are available in the market that makes the customer a bit apprehensive about their attributes, selection, treatment protocols and effects. Laser hair removal is one of the light sources of hair removal.

Light can destroy hair follicles by a number of ways such as thermal, photomechanical or photochemical with generation of toxic mediators like singlet oxygen or free radicals.
Thermal mechanism for hair removal has recently been introduced to induce selective damage to hair follicles. It is based on the principles of selective photothermolysis. This principle predicts that selective thermal damage of a pigmented target structure will result when sufficient quantity of light at a given wavelength is absorbed by the target in a time equal to or less than the thermal relaxation time of the target.

In the visible to near-infrared region, melanin is the natural chromophore for targeting hair follicles. Lasers or light sources that operate in the red or near-infrared wavelength region lie in an optical window of the spectrum in which selective absorption by melanin is combined with deep penetration into the dermis. Therefore, deep and selective heating of the hair shaft, the hair follicle epithelium, and the heavily pigmented matrix is possible in the 600nm to 1100nm region. However, melanin in the epidermis presents a competing site for absorption. Selective cooling of the epidermis has been shown to minimize epidermal injury.

Photomechanical destruction of hair has been attempted with very short nanosecond pulses. This has been done by the help of Q-switched 1064-nm Nd:YAG lasers, with and without carbon suspension. Short pulses used to target hair follicles result in rapid heating of the chromophore (melanin). It leads to photo acoustic shock waves that cause focal photomechanical disruption of the melanocytes but not complete follicular disruption. Therefore, the Q-switched Nd:YAG lasers are not likely to produce long-term hair removal.

A distinction needs to be made between permanent and complete hair loss. Complete hair loss refers to a lack of regrowing hairs. It 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. Histological observations show damage predominantly in hair follicles with large, pigmented shafts, while hair follicles with small hypo pigmented shafts do not demonstrate any morphological change.

Immediately after laser treatment, the hair shaft shows fragmentation with focal rupture into the follicular epithelium and thermal damage to the surrounding follicular epithelium. The extent of thermal damage is dependent on the pulse width but retains confinement on the spatial scale of the follicle itself. Histological changes are almost guaranteed in the person undergoing laser hair removal. However, such form of hair removal should be carried out in the supervision of a qualified dermatologist as it involves considerable degree of expertise.