Laser Hair Removal History
Laser light as a tool for unwanted hair removal was first introduced to US market in 1995, when ThermoLase Corporation (San Diego, CA) received FDA clearance for its hair removal device based on Nd: YAG laser [1].
The method suggested use of infrared (IR) 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 could 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 peak 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 [2-5], the best results were demonstrated with two type of lasers: Ruby laser emitting at 694 nm (red) wavelength and Alexandrite laser that operates at 755 nm (near infrared) line. 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 pigmented with melanin.
This mechanism of selective targeting of the hair follicles was called selective photothermolysis [4] and is illustrated in the Choice of Wavelength section below, where we give more detailed description of the laser hair removal physics.
Since 1997 many companies in 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, that in competing Ruby lasers.
Choice of wavelength
Most of the modern laser hair removal systems operate based on Anderson and Parrish’s 1981 principle of selective photothermolysis [4]. Under the principle of selective photothermolysis, 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 [3,4]. 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 5 mm 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 (see Figure 1) that among popular wavelengths used for hair removal, the wavelengths in 640-780 nm produce the highest temperature rise per unit fluence (laser thermal efficiency) in the hair bulb.
Figure 1. 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 flash lamp-type light sources with very broad emission spectrum).
Currently, only two 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). Recent studies have shown that the clinical results achieved by both types of lasers are on par [3], so the technical differences between two lasers are usually seen as an advantage of the Alexandrite.
Speed and Cost Effectiveness
The practitioners involved in hair removal procedures always pay attention to the time required to perform certain hair removal procedure. 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).
| Spot size | Repetition rate | Area coverage rate |
|---|---|---|
| ∅15 mm | 1 Hz | 1.8 cm2/sec |
| ∅12 mm | 2 Hz | 2.3 cm2/sec |
| ∅10 mm | 3 Hz | 2.4 cm2/sec |
| 9 x 9 mm square | 2 Hz | 1.6 cm2/sec |
| ∅9 mm | 3 Hz | 1.9 cm2/sec |
| ∅7 mm | 5 Hz | 1.9 cm2/sec |
In most laser designs increase of the pulse repetition frequency leads to the lower output energy. This contradiction does not allow achieving high fluence (or energy density) required for efficient hair removal, using relatively big laser beam spot sizes. 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. Though the typical charges for hair removal procedures are relatively high, it may be still difficult to maintain cost efficient operation of the laser if it isn’t fast enough.
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. The data in Table 2 can be helpful in order to estimate required treatment times for different body areas, using known hair removal laser specifications.
| Site | Approximate Size |
|---|---|
| Upper lip | 15 cm2 |
| Face | 80 cm2 |
| Bikini area | 125 cm2 |
| Underarms (2) | 190 cm2 |
| Man’s back | 2750 cm2 |
| Legs (2) | 8100 cm2 |
As an example, it will take DDC Technologies AL-40 Alexandrite laser, (operating at 15 mm spot size, 2 pulses/sec with average 20% overlap) slightly over 15 min to cover the man’s back area. Taking into account some preparation time and possible double treatment in some originally missed areas, the whole procedure can be finished in less than ½ hour.
The only other hair removal method that generally yields permanent results is electrolysis. But even 3-4 laser treatments typically required to achieve permanent hair reduction in the average patient are much less time consuming, than electrolysis. The table below gives a comparison of time between laser and electrolysis to clear a certain body area one time:
| MEN: | Laser | Electrolysis |
|---|---|---|
| Back | 45 min -3 hours | 100-150 hours |
| Shoulders | 10-20-minutes | 25-50 hours |
| WOMEN: | Laser | Electrolysis |
|---|---|---|
| Underarms | 10-20 minutes | 4-10 hours |
| Bikini | 15-30 minutes | 5-10 hours |
| Upper lip | Less than 5 min. | 30-60 minutes |
| Chin | 5-10 minutes | 1-3 hours |
| Legs | 1 ½ -3 hours | 75-150 hours |
References:
- “FDA Approves First Laser Hair-Removal System”, Medical Laser Report V. 9 (5), May 1995;
- J.C. Walling, D.F. Heller and G.J. Fisanick, “Alexandrite Lasers For Medical Applications” SPIE V.1892 Medical Lasers and Systems II, 1993, pp. 52-62;
- James Hsia, Karl Pope, “Comparison of the Candela GentleLASE Hair Removal System with Other Technologies”, Candela Corp. press release, 1998; David Goldberg, Rosaline Ahkami, “Evaluation Comparing Multiple Treatments With a 2-msec and 10-msec Alexandrite Laser for Hair Removal”, Lasers in Surgery and Medicine, v.25, 1999, pp. 223-228;
- B. Finkel, et. al. “Pulsed Alexandrite Laser Technology for Noninvasive Hair Removal”, Journal of Clinical Laser Medicine & Surgery, V.15 (5), 1997, pp. 225-229.