The demand for safe, long-lasting, and effective hair reduction for aesthetic as well as medical indications is on the rise. A variety of options for hair removal are available, such as epilation by plucking or waxing, depilation by shaving, chemical depilatories, electrolysis, eflornithine cream, and laser and intense pulsed light (IPL) systems. A variety of lasers and IPL systems are available and are the best option for long-term hair reduction. The mechanism of action of these systems is by targeting melanin in the hair shaft, follicular epithelium, and hair matrix by emitting light with wavelengths ranging from 600 to 1200 nanometers (nm), which is selectively absorbed by melanin.
Lasers for skin treatment work on the theory of "selective photothermolysis." This term implies a site-specific, thermally mediated injury of microscopic tissue targets by the selective absorption of pulses of radiation by the targets and the chromophores. The natural or artificial chromophores absorb monochromatic or broadband electromagnetic radiation of specific wavelengths. The chromophore employed in laser hair reduction is melanin. Melanin absorbs light in the range of 690 to 1000 nm, and lasers in this range of wavelengths can be effectively used for hair reduction.
An Extended Theory of Selective Photothermolysis
Target absorption may not always be uniform. In these cases, the weakly absorbing parts may have to be destroyed by heat diffusion from the highly absorbing parts. This is the extended theory of selective photothermolysis. This principle is applied to laser photoablation. Melanin content is much higher in melanin-bearing structures like the hair shaft and matrix cells than in the hair follicle. Thus melanin captures energy from the laser and distributes it to the surrounding follicular structures. This results in the destruction of the hair matrix and hair bulge stem cells.
Lasers for hair reduction include the following:
* Fitzpatrick Skin Types
The hair matrix being sensitive to laser treatment in the anagen phase necessitates multiple treatments to treat all hairs during this most sensitive phase. In the initial phase, 4 to 6 treatments spaced 4 to 6 weeks apart are a minimum to achieve adequate results. Subsequently, patients may be maintained with repeat treatments once every 6 to 12 months as small vellus hair may grow back.
Various factors may affect the outcome, such as:
Adjacent epidermal structures other than melanin within the hair bulb can compete for absorption, and may cause laser energy to be absorbed by pigment in the epidermis. This hampers the effectiveness of the treatment and causes adverse effects due to adjacent epithelial damage.
Common adverse effects of laser or IPL-based hair removal include post-treatment erythema, pain, and burning.
More severe adverse effects include blistering, crusting, dyspigmentation, purpura, and sometimes, scarring. Ocular complications due to accidental injury may be seen. Paradoxical hypertrichosis may rarely occur, more commonly in skin types III and with the use of IPL systems.
Selecting the correct lasers with the appropriate parameters, individualized to each patient, is very important, particularly in patients with intrinsically dark skin. Most of the complications are preventable when adequate precautions are taken with adjustment of the fluence, spot size, wavelength, and the use of cooling methods. Thus, it is all the more important that trained personnel with a thorough knowledge of the mechanisms, techniques, and complications, carry out these procedures.