The principle applied for lasting photoepilation by pulsed light is to emit a penetrating ray of red light into the skin where it is absorbed by the dark melanin of hair roots and transformed into heat.

The temperature reached at the root of the hair is such that a coagulation of germ plasm (bud and stem) is produced, incurring the definitive death of hair in the anagenous phase (eliminated by 100%).

Other hairs in the catagenous or telogenous phase continue their growth cycle.

6 to 8 weeks later, these remaining hairs will be in the anagenous phase and may therefore be treated successfully.