Why does hair turn gray as we age?

Hair becomes gray when the pigment-making cells in each follicle gradually make less melanin or stop making it. Without that color, a new strand is mostly pale keratin, so it reflects light as gray, silver, or white.

The change is wonderfully uneven: one follicle may keep its old color while its neighbor grows a bright silver hair. That is why gray often arrives as scattered threads first, then a softer mix across the head over many years.