Laser and light sources produce a bright beam of light that is preferentially absorbed by melanin (the pigment in hair) thus causing damage to the hair shaft and follicle without damaging the surrounding tissue.
Depending on the density of hair, colour of the hair and hormonal factors, the number of treatments required varies from 6-10, spaced 4-6 weeks apart for the face and 6-8 weeks apart for the torso, and 8-9 weeks apart for the legs.
With each treatment there is cumulative damage to the hair follicle and this results in a progressive reduction in the number and diameter of the hairs. There are also different stages of hair growth and hairs in the active growth phase are more responsive to the laser. Both of these facts explain why multiple treatment sessions are required