What mechanisms explain the phenomenon of stress-induced graying of hair, and how does this process relate to changes in hair follicle biology?

Of course, other things can cause grey hair, like the normal aging process and genetic factors. But, there are epigenetic factors, which are above your genes, and you may be able to do something about your genes through your nutrition, environment, and more.

In the hair follicle, you have stem cells, which create pigment. When exposed to chronic stress, you get an elevation of noradrenaline. Noradrenaline is the precursor of adrenaline. They found that noradrenaline causes stem cells to migrate away from the hair root and into the skin. So, you lose your stem cells and, with them, the ability to keep your hair pigmented. The key is to keep your stress low.