Thermal damage patterns of diode hair-removal lasers according to various skin types and hair densities and colors: a simulation study.

Background And Objective: It is important to prevent unwanted side effects of diode hair-removal lasers especially in dark skin tones. This study simulates the thermal damage patterns caused by diode hair-removal lasers in different skin types, hair colors, and hair densities.

Materials And Methods: LITCIT software has been used with the tissue modeled as two components, the skin and the hair. The absorption coefficients of various skin types (f(mel)=5%, 10%, 15%, and 20%), laser parameters, and optothermal properties of tissue were inputs.

Results: For all skin types there was a significant unwanted thermal damage to the epidermis as a result of fluence increase. Using longer pulse durations is accompanied by effective thermal damage to the hair follicle, while preserving the epidermis in skin types II and III, an effect not achieved in darker skins. Regardless of pulse duration, when the distance between hair follicles is ≤ 0.5 mm, there is a significant increase in thermal damage to interfollicular epidermis with high fluences compared with lower hair densities (interfollicular space ≥ 1 mm). In lighter hairs, while using longer pulse durations, higher fluences are needed in order to obtain the same level of thermal damage in the hair follicle as shorter pulse widths.

Conclusions: In lighter skin types, lengthening the pulse duration of diode lasers (up to 400 ms) increases efficacy while preserving epidermis from unwanted thermal damage. However, it is necessary to use lower fluences while using longer pulse duration to avoid irreversible thermal damage to epidermis in darker tones, as is also true for locations with higher hair densities.