ADDITIONAL INFORMATION ABOUT LASER HAIR REMOVAL

1. Laser Hair Removal History
2. Choice of Wavelength
3. Speed and Cost Effectiveness
• Table 1
• Table 2

I. LASER HAIR REMOVAL HISTORY
Laser light as a tool for unwanted hair removal was first introduced to te US market in 1995, when ThermoLase Corporation (San Diego, CA) received FDA clearance for its hair removal device based on the Nd:YAG laser. The method suggested use of infrared (1064 nm wavelength) laser light in conjunction with a topical light absorbing solution. Though the long lasting effects of that first laser hair removal approach were questionable (in terms of its comparison with electrolysis), its speed and virtual painlessness were so attractive that laser hair removal soon became very popular. It was soon found out that best results in hair removal can be achieved only when the unique laser light property is correctly utilized. The fact that laser emits its light energy in very narrow spectral range (usually represented in laser specifications by peek emitting wavelength), makes it possible to effectively deliver laser energy right to the hair follicle, without damage to surrounding skin layers. That's why the search for the laser which would be best choice for hair removal application has started right after the first laser appeared in the market. After number of clinical studies have been performed, the best results were demonstrated with three types of lasers: Ruby laser emitting a 694 nm (red) wavelength and Alexandrite laser that operates at 755 nm(near infrared) frequency and the diode laser (810 nm frequency). The clinical advantage of these two lasers was based on the big difference in absorption between upper skin layers (epidermis) and hair follicles containing hair follicles was called selective photothermolysis and is illustrated in the Choice of Wavelength section below, where we give a more detailed description of the laser hair removal physics. Since 1997 many companies in the USA and Europe introduced new laser hair removal devices. The lasers for hair removal today come in all shapes and sizes. There are also different lasers that use different wavelengths of light. Some utilize a cooling device and some do not. All laser systems emit a gentle beam of light that passes through the skin to the hair follicle where it is absorbed by the hair. Among all these systems the Alexandrite laser based devices have won the biggest market share. The popularity of these lasers is based on preferable wavelength of 755 nm, high energy per pulse, which can be delivered at higher speed from more compact package, than in competing Ruby Lasers.
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II. CHOICE OF WAVELENGTH
Most of the modern laser hair removal systems operate based on Anderson and Parrish's 1981 principle of selective photothermolysis. Under the principle of selective pholothermolysis, when a pigmented target absorbs a particular wavelength of light in an amount of time that is shorter than or equal to the thermal relaxation time of the targeted structure, the targeted tissue will be selectively destroyed without surrounding tissue injury. The absorption properties of the main chromophore of hair follicles - melanin, and surrounding epidermis have suggested that lasers emitting light in red and near infrared spectrum are the best light sources for the hair removal. Since melanin in the hair shaft/bulb is the primary chromophore for laser hair removal and because one of these targets (bulb) may be located up to 5mm below the skin surface, the optimal choice of wavelength depends on both skin penetration depth and melanin absorption. For a typical hair bulb diameter of 0.3 mm located 3 mm below the skin surface, the calculations show that among popular wavelengths used for hair removal, the wavelengths in 640-810 nm produce the highest temperature rise per unit fluence (laser thermal efficiency in the hair bulb).
Temperature rise in a 0.3 mm diameter hair bulb per unit fluence as a function of wavelength. In simple words, the lasers operating at preferable wavelengths can deliver more heating damage to the hair bulb without burning the surrounding skin. This property of the laser light also gives it substantial advantage when laser is compared to non-laser hair removal devices (such as flashlamp-type light sources with very broad emission spectrum). Currently, only three types of solid-state lasers emit light at the appropriate wavelengths and with sufficient output energy for the hair removal procedure. These lasers are Ruby laser (694 nm output wavelength and Alexandrite laser (755 nm central output wavelength) and the diode laser (810nm output wavelength). Recent studies have shown that the clinical results achieved by the three types of lasers are on par, so the technical differences between two lasers are usually seen as an advantage of the Alexandrite.
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III. SPEED AND COST EFFECTIVENESS
The practitioners involved in hair removal procedures always pay attention to the time required to perform certain hair removal procedures. This time eventually determines the cost of the treatment and it strongly depends on the laser performance characteristics. In terms of pulsed lasers there are only two ways to increase the coverage rate of a treatment: increase the pulse repetition frequency (rep. Rate), or increase the spot size. How fast a laser covers a treatment area is a product of the spot size and repetition rate (see table 1).
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Table 1
OPTIMAL COVERAGE RATES OF VARIOUS LASERS

In most laser designs increase of the spot size and pulse repetition leads to the lower output energy. This contradiction does not always allow the laser to achieve high enough fluence (or energy density) required for efficient hair removal, using relatively big laser beam spot sizes or the faster repetition rates. That is why the capability of the hair removal laser to deliver high average power (i.e. high pulse energy at high repetition rates) is the most important factor to consider if one is looking for cost effective system. The typical costs of hair removal procedures for the customers are shown in Table 2 (this data must be interpreted as a general guideline only and does not represent exact costs, special contracts and treatment conditions may exist).
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Table 2
TYPICAL COSTS OF VARIOUS HAIR REMOVAL PROCEDURES

Finally, we can say that actual treatment time depends on the laser hair removal system technical parameters, certain body area being treated, particular patient skin and hair type and practitioner's skills and experience.
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