In mice with a broken Dguok gene, their hair turns gray because the stem cells that give color to hair disappear early, even before the color actually fades.

In mice with a specific genetic problem, hair turns gray because the stem cells that make hair color die off first—not because the color-making process itself is broken.

Going gray might happen because the stem cells that keep your hair colored stop working properly as you age, according to studies in people and specially tagged mice.

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.

When mice experience sudden stress, it causes the cells that give hair its color to panic and leave their home in the hair follicle, burning out too soon and making the fur turn gray forever.

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.