Long-pulsed ruby laser for permanent hair reduction: histological analysis after 3, 4 1/2, and 6 months.

Objective: The histology of hair follicles in both animal and human skin treated with ruby lasers has been evaluated to a limited extent in previous studies. We have previously looked at such follicles up to 2 months after treatment. This study examines the longer-term effects at a microscopic level and attempts to further elucidate the mechanism of ruby laser hair reduction.

Methods: Thirty-six patients underwent 1, 2, or 3 treatments of their axillary or bikini area skin with a 3 milliseconds ruby laser at 10, 20, 30, or 40 J/cm(2). Biopsies were taken 3, 4(1/2), or 6 months after the last treatment and examined histologically. Nine control biopsies were taken from comparable bikini areas of untreated patients and similarly evaluated histologically.

Results: There was a significant increase in telogen compared to anagen follicles in treated skin, which was slightly increased by multiple compared to single treatments, but unaffected by different time intervals since the last treatment. There was also a significant increase in miniaturized compared to terminal hairs in treated compared to control skin, a finding that was further increased with higher energies used. Multiple treatments and time after treatment had a slight, but not statistically significant effect on follicle size.

Conclusions: Induction of telogen in terminal follicles followed by miniaturization appears to be the main mechanism of ruby laser hair reduction.