Define "anagen" phase in hair growth.

The anagen phase is recognized as the active growth phase of hair. During this stage, hair follicles are highly productive, resulting in the generation of new hair cells. These cells keratinize, leading to the elongation of the hair strand and marking significant hair growth. The duration of the anagen phase can vary widely among individuals and different hair types, lasting anywhere from two to seven years or even longer in some cases. This phase is crucial for determining the overall length and health of hair, as it directly influences how much hair can grow before entering subsequent phases of the hair growth cycle. The active growth nature of the anagen phase is what distinguishes it from other phases, such as shedding or resting.