Laser acupuncture is recognized as the biostimulation therapy with a low energy laser, while the mechanism has not been clear. However, in the pulsed laser acupuncture, the thermal stress caused by the photo-acoustic effect is thought to be the dominant factor of the biostimulation.
This paper proposes a method of calculating the spatial distribution of the thermal stress inside a human skin tissue using Hu's model for analyzing the photo-acoustic wave in the liquid. Numerical calculations show that the shape of the thermal stress depends on the absorption coefficient of the laser, that is, the stress due to the CO₂ laser occurs sharply compared with the case of the YAG laser.