HAIR-GROWTH CYCLE AFFECTS HAIR FOLLICLE DESTRUCTION BY RUBY-LASER PULSES

It has been shown that normal mode ruby laser pulses (694 nm) are effe ctive in selectively destroying brown or black pigmented hair follicle s in adult Caucasians. This study investigated how the various stages of the hair follicle growth cycle influence follicle destruction by ru by laser treatment, using a model of predictable synchronous hair grow th cycles in the infantile and adolescent mice. A range of ruby laser pulse fluences was delivered during different stages of the hair growt h cycle, followed by histologic and gross observations of the injury a nd regrowth of hair. Actively growing and pigmented anagen stage hair follicles were sensitive to hair removal by normal mode ruby laser exp osure, whereas catagen and telogen stage hair follicles were resistant to laser irradiation. Selective thermal injury to follicles was obser ved histologically, and hair regrowth was fluence dependent. In animal s exposed during anagen, intermediate fluences induced nonscarring alo pecia, whereas high fluences induced scarring alopecia. The findings o f this study suggest treatment strategies for optimal laser hair remov al.