The anagen phase is the active growth stage of the hair cycle, during which the cells at the root of the follicle divide rapidly to produce a new hair shaft. As these cells continuously multiply and keratinize, they push the hair upward and out of the skin, growing at a rate of roughly half an inch per month. This phase dictates the maximum length of the hair and can last anywhere from two to seven years on the scalp, making it the longest portion of the entire hair growth cycle.

The catagen phase is a brief, transitional stage of the hair cycle that immediately follows the active growth period, typically lasting only two to three weeks. During this time, hair growth comes to a halt as the follicle shrinks and detaches from its blood supply—the dermal papilla—at the base of the root. This detachment turns the strand into what is called a "club hair," keeping it anchored in place while the lower part of the follicle breaks down and prepares for the resting stage

The telogen phase is the final, resting stage of the hair cycle, typically lasting around three to four months. During this period, the hair follicle is entirely inactive, and the fully formed club hair remains anchored in place while the dermal papilla beneath it rests. At the very end of this phase—often categorized separately as the exogen phase—the resting hair naturally detaches and sheds, making room for a new hair to emerge from the follicle as the entire cycle restarts with the anagen phase.