Under normal circumstances hair growth in each hair follicle occurs in a cycle. There are three main phases of the hair growth cycle: anagen, catagen and telogen.
Anagen (active) is the growing phase or when the hair fiber is produced. During anagen, the hair contains an abundance of melanin, the pigment which gives your hair its color. This is the phase during which laser hair removal treatment is most effective.
Catagen (club hair) is the period of controlled regression of the hair follicle. This phase is when the lower part of the hair stops growing, but does not shed, and the follicle is reabsorbed. It will be difficult for permanence to be achieved when the hair is in the catagen growth cycle.
Telogen (tired) is the last of the hair growth cycle. In this resting phase, the old hair falls out in preparation for the development of a new anagen hair. Permanence cannot be achieved when the hair are in the telogen growth cycle.
Remember, anagen is followed by catagen, a period of controlled regression of the hair follicle. Ultimately the hair follicle enters telogen, when the follicle is in a so-called resting state.
Normally this cycle of hair production will continue for the duration of the individual's life. However, other factors can influence, promote and inhibit hair production. How well the laser can eliminate the hairs, depends on the skin type/color, hair type/color and what initially caused the hair to grow.