Anagen Phase

The anagen phase is the active growth stage of the hair cycle during which cells in the hair bulb divide rapidly to produce the hair shaft and its surrounding structures. On the scalp this phase typically lasts from about two to seven years (and can be longer in some people), and at any given time the majority of scalp hairs are in anagen, which is the primary factor that determines potential hair length and overall density.

Shortening of the anagen phase or premature transition to catagen or telogen reduces hair length and density and is involved in conditions such as androgenetic alopecia and telogen effluvium, while some medications and illnesses can cause abrupt anagen loss (anagen effluvium). Clinically, knowing whether hairs are in anagen helps with diagnosis, prognosis, and timing of interventions that rely on active hair growth, and it explains why regrowth after insult can take months to appear.