As we mentioned, there are three main phases of the hair growth cycle; anagen, catagen and telogen with anagen further subdivided into proanagen, mesanagen and metanagen.
Anagen is the active growth phase when hair fibre is produced. Proanagen marks initiation of growth with RNA and DNA synthesis in a follicle which then quickly progresses through mesanagen to metanagen and maximum follicle length and girth. In this mature state of proliferation and differentiation the hair follicle consists of a total of eight concentric layers and melanogenesis (pigment formation) occurs within pigmented hair follicles (more about this when we discuss laser hair removal).
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. The next few pages will show the growth cycles schematically.