There are very many hair removal methods, such as waxing, hair removal cream… However, these methods can only remove hair temporarily and need to be operated repeatedly and frequently, so more and more people are choosing laser hair removal. How to remove hair by laser? Laser is a single wavelength, continuous beam of light with minimal dispersion and high energy. Laser hair removal is based on the theory of selective photothermal action, through reasonable adjustment of laser wavelength, energy, pulse width, etc., targeting the melanin of the hair follicle, light energy is absorbed by the melanin and converted into heat energy to destroy the hair follicle tissue, so that the hair loses its ability to regenerate and achieve the purpose of permanent hair removal, while not damaging the surrounding tissue, and the pain is mild. The reasons why multiple treatments are needed to completely remove hair are: 1. Hair growth is cyclical, i.e., from the anagen phase to the regression phase to the resting phase and then to the anagen phase in a continuous cycle. This change in growth cycle is a continuous process. 2, only the hair in the anagen phase, the hair root and hair bulb parts contain a lot of melanin, melanin can effectively destroy the hair follicle after absorbing the energy of the laser to achieve the purpose of hair removal; 3, in the resting and regressive hair, the hair root and hair bulb contain little or almost no melanin, the laser can not act on the hair follicle so the treatment at this time is ineffective on the hair; the regressive cycle of hair is usually 2-4 weeks, the resting period usually 3-4 months. Therefore, the laser only works on the hair in the anagen phase, that is to say, only on the part of the hair that is visible on the body surface at present, but not on the resting hair. After each treatment, a time interval of 1-1.5 months is needed to wait for the resting hair to grow out before the second hair removal. Therefore, one treatment cannot solve the problem completely. Generally 3~5 hair removal can reduce the hair by more than 90%. Therefore, it is usually necessary to go through several treatments.