When Q-switched ruby lasers were employed in large numbers in cutaneous laser surgery another serendipitous enlightenment occurred. The immensely powerful though short bursts of energy generated to fragment tattoo particles were noted not only to vaporize darkly pigmented hairs but also to bleach them below their follicular exit and even to inhibit their reappearance. Studies by Dover et al. (271) in 1989 had shown selective pigment cell damage in follicles from this laser, which caused the leukotrichia. It seemed that laser energy had reached a portion of the pigmented hair bulb and disrupted it enough so that it might act also as a depilatory, or better still, a nonscarring permanent or epilatory instrument. The financial appeal of entering the 6 billion dollar-a-year industry of cosmetic hair removal was too enticing for laser manufacturers to avoid. Truly medical applications such as treating disfiguring hirsutism in women or pseudofolliculitis barbae in men (and rarely women) were an additional potential benefit.
Thermally nonselective but effective destruction of hair follicles in hair-bearing grafts, or for trichiasis, had been reported as early as the 1970s (393 -396) but hair removal by thermal damage confined to the hair follicle governed by the principle of selective photothermolysis had not been attempted.
The first FDA-approved laser for hair removal did not depend on the pigmented hair as a target but instead a patented mineral oil lotion was used containing carbon-based material, which was presumed to seep into the follicles after waxing immediately prior to massaging of the lotion and thus provide a target for the laser. Presumably, the mechanico-acoustic wave appearing after the laser impact would then disrupt the base of the follicle so that the loosened hair would fall out and the damaged follicle would no longer produce hair. In 1995 Goldberg and coworkers (397,398) presented the first studies showing very short-term efficacy. Hyperbole from the mass media was unfortunately not countered immediately; neither the short 12 week duration of the study nor the low 25% hair loss at that time was widely publicized. The hairs grew back, in fact most of them by 3 months, although more slowly in lased sites, and all of them grew back (399) by 6 months. Nanni and Alster (399) also demonstrated that the scientific principle behind this laser was flawed in that the carbon suspension was not required for hair removal since, at 1 month, waxing plus laser alone was equivalent to carbon-assisted laser removal. Nevertheless, these flawed data became a public mantra that laser removes hair. The public was led to believe by the mass media that this was permanent hair removal done quickly, painlessly, and without potential for scarring, all unlike traditional electrolysis. The public again had unrealistic expectations driven by laser hyperbole and many patients became dissatisfied with this very expensive and temporary procedure. When educated properly about the relative long-lasting effects and the apparent diminution of caliber of hair, most of the treated public was content.
Also in 1995, Grossman et al. (400) reported their preliminary results with normal mode ruby laser in black-haired dog skin and found that this laser with a pulse duration of 0.297 ms, shorter than the estimated thermal relaxation time for a 200-300 mm hair follicle of 40-100 ms (401), could produce selective thermal damage to the hair follicle. They soon followed this abstract with a published report on 13 patients treated only once with normal mode ruby laser (402), noting that four of them had less than 50% regrowth after 6 months. They also claimed that "selective thermal injury to follicles was observed."
Unfortunately, only horizontal sections of the upper follicle were shown. It was years before any investigator presented vertical sections exhibiting the nature of damage to the hair bulb and still no one has shown the numbers of scarred or atretic follicles on vertical section. Controversy again reigned because of the claims of "permanent" hair loss by these and other authors and the lack of both clinical and histologic proof (403). In mouse studies the Wellman Lab showed in 1998 that only anagen hairs were affected by ruby laser. This suggests that at least for mice the pigmented bulb and not the stem-cell-containing bulge was the ruby laser's target (404). Only one of Grossman et al.'s original 13 patients had lost all hair at 2 years' follow-up and the four with diminished hair had no decrease in actual hair counts; histology showed hair follicles but with evidence of some miniaturization with vellus hairs replacing terminal hairs (405). Subsequent studies demonstrated long-term hair reduction with several long-pulse lasers, though patients required a series of treatments. The long-pulsed ruby, alexandrite, diode (810 nm), and Nd:YAG (1064 nm) are widely used for long-term hair reduction (406). In 1999 the word "permanent" was redefined in an Orwellian fashion by the FDA to no longer mean "forever" but, for the hair follicle, to mean absence of a visible hair for a period longer than one estimated anagen-telogen growth cycle for a particular body region. Such language manipulation served as a marketing ploy that only confused the public more.
One positive redirection concurrent with attempts to make hair removal safer was a renewed interest in thermokinetics and protection of tissues not by selectivity of absorption and nonabsorption but protection even in the face of absorption by both the target and the nontarget. Because the thermal relaxation time of the pigmented epidermis is estimated at 3-10 ms, the epidermis is also a target for the ruby laser and with high fluences of 20 J/cm2 or more required for hair removal, significant destruction of the epidermis would occur if simultaneous cooling devices were not used.
If two tissues shared too many common absorbents but were either physically different in size or were separated by some distance in the skin one could select pulse durations intermediate between each tissue's estimated thermal relaxation time. One could preferentially heat smaller targets faster and larger targets slower to spare inversely their corresponding larger or smaller coabsorbers. One type of thermokinetically set alexandrite hair removal laser was manufactured which lengthened its pulse duration in order to deliver its energy over a longer period to the hair bulb and follicle and over too long a period to appreciably affect epidermal melanin in light-complexioned patients. Unfortunately, this theoretical enhancement did not provide a marked clinical difference (407). Such selectivity of longer pulse durations for larger targets to also protect smaller targets has more recently been employed for long-pulsed diode hair removal lasers for very darkly pigmented patients (408).
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