The photothermal effect is the main mode of action of current clinical laser applications. When heat energy acts on the surface of a tissue, it will directly heat the tissue within an absorption length. The heat is also conducted to the surrounding tissue through thermal relaxation and is not conducted to adjacent tissues. The heat vaporizes or removes tissue near the surface. The rate of tissue removal depends on the concentration of laser energy in the tissue. The higher the laser power, the faster the water vaporizes and the tissue is removed, and the minimal heat damage removes the tissue faster than the surrounding tissue underneath the heat conduction, which ensures that the coagulation effect is limited to the absorption length of the laser.

Generally speaking, after the first laser irradiation, the skin surface will appear white bubbles. This change indicates that the water in the cells has vaporized, leaving dry protein debris. When these debris are washed away with salt water, obvious skin shrinkage will occur. The skin has a yellowish appearance, and these features are more obvious in thicker skin such as around the mouth. There is significant shrinkage in thinner skin areas such as the upper eyelids without obvious yellowing of the tissue. After three or more irradiations, some yellow-brown dehydrated protein denatured substances can be seen. These substances represent the denatured collagen of the dermal reticular layer, and will appear further thereafter. Carbonization and heat dispersion lead to tissue necrosis.