Does low penetration of human skin by the normal mode ruby laser account for poor permanent depilatory success rates?

Studies reported to date have shown a good depilatory response from patients treated with the normal mode ruby laser (NMRL) over 12 weeks, but a low response over a time period greater than this. Previous publications have suggested that this could be accounted for by the apparently poor skin penetration of laser light and so this study attempted to assess whether this was indeed the case. Skin samples of varying thicknesses were taken from six Caucasian patients and their depths measured. Each was laid individually on an energy meter before having pulses from an NMRL compatible with clinical doses (4.75 J/cm2, 9.24 J/cm2 and 13.41 J/cm2) fired on the epidermis. Several samples had the laser fired repetitively on the surface to assess whether this caused any change in laser/skin fluence depth profiles. Repetitive firing of the NMRL on the epidermis of skin samples did not alter the energy recorded by the meter beneath. The fluence/depth profiles were constructed showing the majority of energy was lost within the first 1 mm of the skin surface (50%) which then further reduced over distance but at a much slower rate. The maximum depth of penetration was 14.8 mm (SD +/- 0.478) which appeared to be a function of wavelength and not fluence. The results suggest that laser penetration of skin should be adequate for generating enough heat at the hair bulge and bulb, potentially causing permanent damage. The implications of this study are that it is probably the presence of the correct chromophore in large enough amounts which is required for successful permanent depilation to occur.