During which growth phase does the hair become fully keratinized?

The anagen phase is the active growth stage of hair follicles, where the hair is formed and becomes fully keratinized. During this phase, cells in the hair bulb divide rapidly, pushing older cells upward. As these cells move away from the follicle, they undergo a process of keratinization, where they fill with keratin, a fibrous protein that forms the structure of hair. By the end of the anagen phase, the hair shaft is fully formed, and the keratinization process is complete, resulting in a strong, mature strand of hair.

In contrast, during the telogen phase, hair is in a resting state and is not actively growing or becoming keratinized. The keratogenous phase is not commonly classified in hair growth terminology and is not recognized as a specific growth stage. The catagen phase is a transitional stage where hair growth stops, and the follicle begins to shrink, making it unsuitable for the full keratinization of hair. Understanding these phases highlights the importance of the anagen phase in the hair growth cycle and its role in producing healthy, keratinized hair.