“Human aging is not a linear, fixed biological process,” says the coauthor of a new study.
Pivotally, the researchers found that some participants’ gray hairs naturally reverted to their prior color when lifestyle stressors dissipated. One participant went on vacation, and five hairs returned to dark color during the holiday. Once beyond the scalp, the hair cannot change color, but newly growing hair in the follicle can. The effect is thought to be from stress changes in mitochondria, and you can see what it looks like in a video here.