At what time can a terminal hair turn back to a vellus hair?

The concept of terminal hairs reverting to vellus hairs is rooted in the understanding of hair growth and the phases of the hair cycle. Terminal hairs are thicker, coarser, and darker, while vellus hairs are finer and lighter in color. Once a hair has transitioned to a terminal phase, it typically will not revert back to a vellus state. This is primarily due to the hormonal and physiological changes that lead to the growth of terminal hair, particularly in areas where hormonal influence is significant, such as during puberty.

The hair growth cycle consists of several phases, including anagen (growth), catagen (transitional), and telogen (resting). Terminal hairs are generally considered permanent, especially in areas influenced by androgens, such as the scalp or beard areas in males and females. Hair follicles that have transformed from vellus to terminal usually remain terminal as long as the influencing factors, like hormones, are present. Therefore, it is accurate to state that terminal hair does not revert back to vellus hair, affirming the idea that this transition is irreversible in the context of typical hair growth and cycling.