Successful reduction in skin damage resulting from exposure to the normal-mode ruby laser in an animal model

Abstract

Normal-mode ruby laser (NMRL) irradiation of skin has now become an acceptable method of producing depilation. However, side effects, which include superficial burning and changes in skin pigmentation, still occur and, although temporary, can be distressing to the patient. This paper reports a method by which the skin can be protected (or preconditioned) from damage during NMRL treatment by pre-heating to a lower, non-damaging level prior to irradiation. Using the black-haired mouse (C57B1/10) as an animal model, an appropriate 'preconditioning' temperature was established by exposing the mouse skin to a range of temperatures, taking biopsies and staining the skin immunohistochemically for heat shock protein 70 (HSP 70) expression within the keratinocyte cells. Increased HSP 70 expression is stimulated by exposure to environmental stressors such as heat, so it was hypothesised that its increased expression conveyed increased cellular protection. The appropriate temperature (45 degrees C for 15 min) allowed for the superficial skin cells to be protected (as assessed by maximal HSP 70 staining) but undamaged (as assessed by haematoxylin and eosin staining), leaving the target hair-producing cells unprotected. Eight mice (16 flanks) were then exposed to this preconditioning temperature (eight of the flanks being growing-hair sites and eight resting-hair sites) and 5 h later exposed to a laser fluence known to cause mild skin damage and depilation (6J/cm2). This exposure was to both the preconditioned and the adjacent non-preconditioned sites. A statistically significant reduction in skin damage (P <0.001), as measured by the time taken to heal and noted both clinically and histologically, was seen in the preconditioned sites in resting-hair regions but not in growing-hair regions. Depilation, established over an 8 week period, was successful in growing-hair regions within both preconditioned and non-preconditioned sites, but complete hair regrowth had occurred in preconditioned and non-preconditioned sites within resting-hair regions by 5 weeks. The latter finding was consistent with work already reported suggesting that NMRL-assisted depilation in this animal model is not successful for hairs in the telogen phase. Successful preconditioning of mouse skin prior to laser exposure appears to reduce NMRL-induced skin side effects. In addition, the technique does not appear to adversely affect successful depilation.