Does Pulse Duration Influence Efficacy of Photo-Epilation?

Abstract

Background and objectives: There are many photo-epilation systems on the market. Many different lasers and flash lamps are used to reduce unwanted body hair. Photo-epilation has become a successful method to reduce hair. But until now there has not been much documented data about treatment parameters. To protect the epidermis the thermal relaxation time (TRT) is said to be the right parameter to determine the pulse duration. This comparison study evaluates different pulse durations between 10 and 40 ms and their influence on efficacy of photo-epilation. Patients and methods: 9 volunteers were treated at 4–6 weekly intervals on 16 test areas on body sites with hypertrichosis (legs, back) with the alexandrite laser EpiLaseTM. Treatment was performed with four different pulse durations that were combined with 4 different energy densities: there were all possible combinations with 10 to 40 ms and 10 to 40 J/cm2. Hair density was evaluated before the first and following every treatment. Hair loss was calculated for each test area in relation to the reference value at the beginning of treatments. Statistical evaluation (p) was done with the Friedman test for several paired groups and the Wilcoxon rank test for two paired groups. Results: Patients were treated on average 4.4 times (rank 3–6) until at least one testing area had reached a sufficient hair reduction. Hair loss between 49 and 63% could be reached. Concerning the efficacy of photo-epilation the tested pulse durations between 10 and 40 ms were not statistically significant different. Conclusion: According to these results it can be assumed that using one of the examined pulse durations does not affect the efficacy of photo-epilation. Longer pulse durations are a great benefit for patients with thicker hair or darker epidermis as time that heats up the target structure (hair follicle) is much longer and the epidermis with shorter TRT cools down in the meantime which is an optimal prevention of side effects. The TRT of epidermis lies between 3 and 10 ms which is clearly shorter than all pulse durations being used in the study. The results encourage us to choose the optimal pulse duration within these limits (10–40 ms) according to the clinical demands (defined by pigment content of epidermis and follicle).