Efficacy of Thin Hair Removal by Dynamic Application of 810-nm Diode Lasers: In Silico and Clinical Comparative Study of Two Laser Powers: 4,800W and 1,000W

Photoepilation of thin hair still represents a challenge for aesthetic medicine. Current commercially available photoepilation devices present limitations for thin hair removal, where efficacy mainly depends on parameters like pulse duration and applied fluence. Objective: This study aims to verify the hypothesis that a dynamic mode (multiple passes with a low fluence and high repetition rate) using a short pulse duration provides better results than longer pulse durations, while still being safe and comfortable. Materials and methods: In order to define the best parameters for the laser set-up, we hereby provide an in silico study as well as a prospective clinical comparison of the efficacy of thin hair removal using the dynamic mode. Short laser pulses with a high laser power (3 ms with the 4,800W, 810-nm Primelase device) as well as longer pulses with a moderate power (11/14 ms with the Primelase device adjusted to 1,000W), reaching identical fluence doses, have been applied in three sessions in a side-by-side study with fourteen subjects on different parts of the body. The efficacy, side effects, and degree of satisfaction of the subject and investigator were assessed. Results: The results predicted by the simulation were corroborated by the clinical data. Using the shortest pulse duration, simulations revealed an average improvement of 15% with original-size hair, and a significantly greater improvement of 21% with the residual thinned hair. Hair counts performed three months after the third treatment showed an overall main hair reduction of 64% on the side treated with the pulse duration of 3 ms, and 55% on the side treated with longer pulses of 10 ms and 14 ms (which represents a 16% greater efficacy with 3ms, with a p-value of <0.024), with a maximum difference of 73% and 46% respectively (59% improvement) in the upper leg where the hair is thinner. The investigator rated 64% of the areas treated with 3 ms as producing good results, compared to only 36% of the areas treated with 10 and 14 ms (p<0.019). In addition, only mild and temporal side effects were reported, without remarkable differences between both sides. Conclusions: This clinical study corroborates the results of the simulations which predicted that the dynamic mode of the 4,800W diode laser device would be more effective than other systems with less power, while also being comfortable and safe. Nevertheless, more subjects as well as more sessions and an evaluation of long-term results would be needed to validate the simulations that predict even better results for the residual thinned hai