When HYF thermal stimulation is applied to the dermis layer where fibroblasts are located with a cartridge with a depth of focus of 3.0 mm, the wound healing power that tries to repair the heat-damaged part and its surroundings works. Therefore, it can promote the accumulation of collagen and elastin to keep the skin firm and fresh, so it can be expected to have the effect of firming the skin, shrinking pores, and lifting up.