In mice, when a specific gene called Bcl2 isn't working, the stem cells that make pigment die off when the hair cycle pauses, but the mature pigment cells stay alive — showing that stem cells really...

When a certain gene called Bcl2 isn't working right in mice, the stem cells that give rise to hair color die off when hair follicles go dormant, but the actual color-making cells are fine—this leads to hair turning gray faster.

As we get older, the cells that give hair its color start to die off because of stress and lower levels of a protective protein, which is why hair turns gray and doesn’t grow back colored.