Hair root has a 3-year growth cycle of two processes (catagenlasting approximately 2-3 weeks and telogenlasting for approximately 3 months). There are generally two factors we consider when removing hair (which also affect the number of sessions): 1) the growth stage of the hairs, and 2) the area of removal.
Only growing hair is treated, which is why most patients receive at least 5 sessions of treatment (with 4-8 weeks in between). It will remove 90-95% of the hair you wish to remove.