Technology guide
The hair growth cycle: why several sessions are needed
Each hair follows its own rhythm, and the laser can only destroy those that are actively growing. This is the key to explaining to your clients the number of sessions and the intervals between them.
Three phases
The anagen phase is the growth phase: the hair is pigmented and firmly attached to its root. The catagen phase is a short transition during which the hair detaches. The telogen phase is a resting phase: the hair is detached and almost unpigmented, before it falls out.
Why only growth matters
In the anagen phase, the hair contains a lot of melanin and remains attached to the papilla, the structure that nourishes it: the heat produced in the hair reaches the cells that produce it directly. In the resting phase, the hair is pale and away from the papilla: the laser has almost no hold on it.
What this means during a session
At any given moment, only some of the hairs in an area are growing. Each session treats this fraction; subsequent sessions catch the hairs that have entered the growth phase in the meantime. Increasing the power does not reduce the number of sessions, it mainly increases the risk of burns.
Spacing sessions according to the area
The pace varies by area. The source indicates 4 to 6 weeks for the face, legs, arms and nape of the neck, and 6 to 8 weeks for the underarms, bikini line, back and chest. Coming back too early reduces effectiveness.
Why 100% does not exist
Follicles are not synchronised, some hairs have little pigment and hormones can reactivate remaining follicles. Fine, sparse regrowth, sometimes years later, is normal: a few maintenance sessions are then enough.