Prospective ex-vivo study on thermal effects in human skin phototypes II, IV and VI: a comparison between the 808, 1064, 1210 and 1320-nm diode laser.

Background: Laser Assisted Skin Healing (LASH) was first introduced in 2001 by Capon and Mordon to prevent keloids and hypertrophic scars. LASH requires homogenous heating throughout the full thickness of the skin around the wound. However, LASH therapy with 808-nm diode laser is deemed to be only applicable for phototype I-IV due to melanin absorption. This prospective ex-vivo study aims to evaluate the thermal effects of different wavelengths (808, 1064, 1210 and 1320 nm) on human skin phototype II, IV and VI.

Material And Methods: Laser shots were applied on skin explants phototypes II, IV and VI. The following laser settings were used: 808, 1064, 1210 and 1320-nm diode laser, Spot size 20 × 3.7 mm, Power 3 W, Irradiance 4 W/cm², 50 shots for each phototype and wavelength. The surface temperature at 2 and 4-mm depth respectively was evaluated by an infrared camera and a low inertia micro thermocouple.

Results: For the 1064, 1210 and 1320-nm wavelengths, the temperature gradient between the surface and 2-mm depth after an irradiation time of 15 s was less than 4.0°C for each phototype. For the 808 nm, the gradient was 0.8°C and 4.4°C in phototype II and IV respectively, but reached 17.2°C in phototype VI. Strong absorption by melanin of skin phototype VI induced unwanted temperature increases at the dermis-epidermis junction, making this wavelength unsuitable for LASH therapy for this phototype. Among the three other wavelengths, the discussion section indicates strong blood absorption at 1064 nm and presents both 1210 and 1320 nm as excellent compromises for LASH therapy across the whole range of phototypes.

Conclusion: Being poorly absorbed by melanin, both 1210 and 1320-nm wavelengths ensure homogeneity of temperature throughout the full skin explant thickness. Their possible utilization for efficient LASH therapy should now be confirmed by prospective in vivo studies.