The stem cells in any hair follicle generate only a certain amount of melanin pigment throughout their lifetimes, so as you age, your hair color wanes. Eyelashes are typically thicker and coarser than the hair on your head, and usually are dark. This combo means they stave off going gray for longer (as does other coarse body hair, like pubic and underarm hair). In fact, your eyelashes could retain their color for decades longer than your locks.

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