It is possible to reverse the process of hair graying by reducing one's stress level, provided that you intervene quickly before reaching an irreversible threshold of biological aging.

noli's read

This claim is based on a highly innovative observational and mathematical modeling study conducted by Rosenberg et al. (2021) in the journal eLife. The researchers effectively demonstrated, using high-resolution imaging technology, that some gray hairs can naturally regain their original pigmentation during periods of relaxation, such as vacations. Nevertheless, it should be noted that these observations are based on a very small sample size of only 14 participants aged 9 to 39. While this discovery fascinatingly proves that graying is not a one-way street, extrapolating these results to promise rejuvenated hair through stress management is premature. The study clearly specifies that this reversibility only applies before a certain threshold of cellular maturity, effectively excluding individuals whose hair has been gray for a long time or due to age.

the sources

No named source held this one up — that absence is part of the verdict.