Theoretically speaking, laser hair removal is permanent, the absolute meaning of one does not grow in actual operation is impossible, even if there is a small amount of residual hair, it is also finer and softer, the color is very light state, the final effect is very satisfactory, can achieve permanent effect. The principle of laser hair removal is based on the theory of selective photothermal action, there is abundant melanin in the hair follicle and hair shaft, these melanin cells can absorb laser energy into heat, so that the local temperature rises rapidly, destroying the hair follicle tissue and removing the hair so that it will not grow again. Choosing the right wavelength of laser can destroy only the hair follicle without damaging other surrounding tissues, such as sweat glands which are completely unaffected and still able to sweat normally. It should be noted that hair growth is cyclical, only in the anagen phase, the most melanin, the most sensitive to laser; regression and stationary phase is not obvious to laser action, so hair removal requires multiple treatments. Different parts of the hair, the growth cycle is different, the interval of treatment is different, with the guidance of professional physicians, after a certain number of treatments, the number of hairs in the treatment area can be sharply reduced. Due to the different color and density of hair, laser hair removal requires different treatment times and final effect, for example, the hair of armpit, torso and limbs, 3-6 times can achieve better effect; the effect of upper lip hair treatment for women is poorer and requires more treatment times, and it needs to increase the number of times of hair removal to achieve satisfactory effect.