Does finding a gray hair stress you out? Some people fret over each new one that pops up while others simply embrace it. But no one really knows when it will happen or why. Until now? Researchers at NYU have unlocked new evidence as to why human hair loses its natural color over time.

The new study, conducted using mice and published in Nature, a peer-reviewed scientific journal, closely examined the melanocyte stem cells known to control hair color. Earlier in life, these cells can be remarkably dynamic, but with age, as hair is lost and regrown, these stem cells tend to slow down. And they get trapped in what's known as the hair follicle bulge—meaning they don't get a chance to finish the job they were created to do.

In other words, when those melanin-producing stem cells stop functioning properly, your hair goes gray. The study is being heralded as a breakthrough of sorts—providing a clearer picture of the cellular glitches responsible for turning us into silver foxes.

Before, scientists had assumed that gray hair was likely the result of that pool of melanocyte stem cells simply running dry. And while the study was conducted with rodents, the researchers say their findings should be relevant to how human hair gets and loses its color. What's more, they hope their findings could be a step toward preventing or reversing the graying process.

With the greater understanding of the stalled-out cells and their probable responsibility for loss of hair color, researchers are now focused on how to get the McSCs back on track. According to lead researcher Professor Mayumi Ito, PhD, the task is “to investigate means of restoring motility of McSCs or of physically moving them back to their germ compartment, where they can produce pigment.” If they find a way to get them moving again (which appears to be entirely possible), it could mean a lot less hair dye in the world.