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.

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 age, the stem cells that give color to our hair can start acting up — they might turn into pigment cells too soon or in the wrong place, which could be why our hair turns gray.

As we get older, the stem cells that keep our hair colored might stop working properly because of problems in their internal repair system, and once they're gone, our hair turns gray for good.

As we age, damage from oxidative stress can harm the cells that give hair its color, especially because the body’s natural antioxidants weaken over time — this leads to grey hair.

When the stem cells that give your hair its color get worn out or change too early because of stress in the cells, they stop making pigment, and your hair turns gray permanently.