Catagen is the transitional phase in the hair growth cycle that follows the active growth stage, known as anagen. During this period, which lasts about two to three weeks, the hair follicle begins to shrink, and the hair strand detaches from the blood supply. This marks the end of the hair's growth. In catagen, the hair stops growing and prepares to enter the resting phase called telogen. This phase is crucial for the natural cycle of hair renewal, allowing new hair to eventually replace the old, shedding hair. Understanding catagen helps in comprehending hair health and growth patterns.