Final answer:
The active growing stage of hair is referred to as the anagen phase, which typically lasts from 2 to 7 years and is characterized by rapid cell division within the hair follicle.
Step-by-step explanation:
The active growing stage of hair is called the anagen phase.
During the anagen phase, cells within the follicle divide rapidly, leading to the production of new keratinocytes and the elongation of the hair shaft.
This phase typically lasts from 2 to 7 years.
The subsequent stage, known as the catagen phase, is a transitional period that marks the end of the active growing period, and lasts for about 2 to 3 weeks.
The telogen phase is the rest period, during which time there is no new hair growth and the old hair is eventually shed.
The human scalp typically loses about 50 hairs per day, with new growth originating from the hair matrix, containing a layer of basal cells which can generate a new hair follicle.