The hair follicles that absorb energy from the laser will be damaged. Hairs that were present in the follicles at the time of treatment will fall out over the next couple of weeks and future hair growth will be impaired. Since not all hairs are actively growing at the same time multiple treatments are required for optimal results.
As the follicles in the transitional and resting periods return to the active growth phase, you may notice some hair regrowth but not as thick as it was before the treatment. This regrowth will become thinner and lighter with each subsequent treatment until there is little, to no hair at all. The number of treatments required for permanent hair loss depends on the client and the treatment area.