Mouse pigment stem cells don't have a special group that never changes; different cells make Oca2 protein in each hair growth cycle.

When mouse hair is repeatedly plucked, more pigment cells get stuck in the bulge area (from 10% to 50% of follicles), and these stuck cells don't help make new hair color.

Mouse pigment cells that make Oca2 protein can turn back into stem cells after moving to the bulge area of the hair follicle.

When mouse hair starts growing, pigment stem cells in the hair germ turn on color-making and branch-related genes before they divide.

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.

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.