Mechanisms of cytotoxic chemotherapy-induced alopecia

Hair follicles are continuously cycling with periods of active growth characterized by cell differentiation and division (anagen), regression (catagen), and rest (telogen). After the rest period, hair is shed as part of the normal hair cycle (exogen). The majority of follicles are in the active growth phase. The main damage from chemotherapy is during the anagen (growing) phase, while chemotherapy also increases shedding during the resting phase.