All hair, regardless of the area of the body, has a different growth cycle. Eyelashes and eyebrows, for instance, grow for about four months and then are shed. The life span of a human scalp hair is from two to four years. After the hair is sloughed off, the follicle becomes dormant for a period varying from a few weeks to several months, and then begins once again to produce hair. Since only visible hair can be treated, the initial treatment period for any given area is four months.
Much of the perceived “re-growth” that occurs during treatment is really hair emerging from dormancy. Once this hair becomes visible, it can be treated for the first time.