Duration of this stage directs the length of the hair and varies considerably according to hair site.
This stage lasts about 3 weeks over all hair sites
Duration varies according to hair site
The anagen phase sees the growth of new hair and the laying down of pigment. It commences in the secondary hair germ at the level of the bulge about 1.5mm below the surface of the skin. As the hair grows the hair bulb moves deeper into the dermis and down to the level of the subcuta neous fat. This can be between 2mm and 7mm below the level of the skin’s surface. The depth is location dependent. Permanent hair removal is most successful when performed on hairs in the anagen phase of the cycle.
The cessation of this growth phase is governed by a number of factors that are still being investi gated but are thought to be attributable to multiple growth factors. Whether the hair is in anagen phase when treated has a bearing on the frequency of treatments and the effectiveness of treatments using IPL and laser.
The anagen phase is followed by catagen, which sees a controlled destruction (apoptosis) of fol licular cells in the inferior segment. This results in the movement of the base of the follicle to the level of the bulge (it becomes shorter and returns to its position where it started anagen) and the formation of a secondary germ from the dying epithelial column. Melanin production ceases and there is death of some melanocytes. If the dermal papilla does not reach the base of the bulge the hair is lost entirely.
Telogen (the resting phase) results in a club hair. This is the time at which a new hair begins to grow from the hair follicle. As it grows upwards the old hair will be shed naturally or may be pulled out, which happens easily and painlessly with telogen hairs. These are the hairs that come out when washing or brushing. Shedding is part of the normal process of the replacement of old hair with new. At any one time, around one in ten of the follicles are in the shedding phase. The new hair emerges from the same opening at the surface of the skin as the old one, and the hair cycle begins again.
The matrix is not the only growth centre in the hair follicle. Through careful experimentation involving the removal of the lower one third of the hair follicle this has been established. This showed that the outer root sheath and the adjacent mesenchymal layer from the lower follicle could regenerate the hair follicle.
The location of the slow-cycling stem cells is also of interest. A group of these cells can be found within the outer root sheath in the area of the bulge. This is at the lower end of the permanent portion of the hair follicle. It is thought that they interact with the germ cells in the growing papilla to promote the downgrowth of the hair follicle seen in early anagen.
It is now thought that after epilation injury to the bulge cells, transient cells in the secondary germ are able to differentiate and repopulate the bulge area. This has implications for the permanency of hair removal. It means that the electrolysis treatment must destroy more than one growth centre within the hair follicle – the matrix and the stem cells in the bulge area.