During laser hair removal, a laser light is directed into individual hair follicles. The laser light will heat the pigment within the follicles, causing its disruption and dispersion. The hair follicle's pigment will be broken into multiple tiny parts, which are harmlessly absorbed into the body and then eliminated. Since the hair follicle is then damaged, it will not be able to grow new hair in the future.
There are four separate stages of hair growth. The first stage is called early anagen, which is the stage during which the hair is just starting to grow in. In the second stage, anagen, the hair is actively growing. In stage 3, catagen, the hair is regressing. Finally, in stage 4, telogen, the hair is resting and there is no new growth at all. Laser hair removal targets hair at its anagen phase, meaning that it only impacts the actively growing hair.
Since laser hair removal targets just the actively growing anagen phase hair, about 25 percent of the hair is removed during each laser hair removal treatment. Therefore, it will usually take a total of around 4 appointments to fully address all the hair as it comes into its growth stage. Laser hair removal appointments are scheduled at a minimum of a month apart so that the new hair has time to grow in.
As long as the hair has been removed during the active growing phase, the hair removal should be permanent. Sometimes hormonal changes can cause new hair growth, however. In this case, a patient may need a laser hair removal touch-up about two years after their initial set of treatments.