There are a lot of places who do hair removal (or reduction as we like to call it) with different messages to clients. Some promise to be able to do a permanent hair removal in one treatment which of course is not possible. The reason for that is that hair grows in stages: Anagen is the active growth phase, catagen is the transition phase, and telogen is the resting phase. The duration of the anagen phase governs the length of hair at different body sites.
Lasers or Light treatments are truly effective in only the anagen phase, when the melanin content is at its highest. The ratio of anagen follicles to telogen follicles varies with body location. Because not all of the hairs are in the anagen phase at any 1 time, laser or light treatments must be repeated to capture the new hairs coming into the anagen phase. At any one time, only 30% of the hair is in the anagen phase.
The timing of treatments is important because hair should be treated during the anagen phase. This phase is short (6-12 wk) for hair on the head, and treatments are spaced a month apart. On the trunk, the telogen phase lasts 12-24 wk, and 2-month spacing is best.