Good question. Hair grows in three cycles, Anagen, Catagen and Telogen. The active state of growth is the Anagen phase. The hair is ‘alive’ in this phase, i.e. it is attached to the bulb of growing cells in the hair follicle. Laser hair removal is only effective during this cycle of hair growth.
It is important to note that each individual hair may be in a different hair growth cycle. If the hair is in either the Catagen or Telogen phase, they will not be successfully targeted and therefore will only be treated in subsequent sessions.
As such additional treatments are needed for each follicle to be treated whilst in the Anagen phase.
The typical number of treatments range from 6-12 and is dependent on the area being treated, hormones, lifestyle, as well as medications and supplements being taken.