Once a vellus hair is transformed into terminal hair, how long does it take to revert back?

Once a vellus hair transforms into terminal hair, this change is generally considered permanent. Vellus hair is fine, light, and short, while terminal hair is thicker, darker, and longer. The transformation typically occurs due to hormonal changes, particularly during puberty or other periods of significant hormonal shifts.

When a vellus hair becomes terminal, the physiological changes that facilitate this transformation, including changes in hair follicle structure and the hair's growth cycle, indicate that reverting back to vellus hair would not occur spontaneously or within a short timeframe. The hormones that cause this transition often remain influential over a person's lifetime, particularly for regions of the body that are impacted by androgenic stimulation. As such, while some individual factors may influence hair regrowth over time, once the transition to terminal hair occurs, it does not revert back to vellus hair under normal circumstances, making the option indicating "never" the correct choice.