When Marie Antoinette was captured during the French Revolution, her hair reportedly turned white overnight. In more recent history, John McCain experienced severe injuries as a prisoner during the Vietnam War and lost his hair color.
These incidents urged scientists to connect stressful experiences with the phenomenon of hair graying. However, the reasons remained a mystery until recently.
Harvard University scientists have discovered how the process plays out, and published their findings in the Nature Journal.
A team of researchers led by Dr. Ya-Chieh Hsu, an associate professor of Stem Cell and Regenerative Biology at Harvard, found that stress activates nerves that are part of the fight-or-flight response, which in turn causes permanent damage to pigment-regenerating stem cells in hair follicles.
Researchers first had to narrow down which body system was responsible for connecting stress to hair color, including the possibility of a link between the gray hair and Cortisol, as stress always elevates the levels of the hormone.
They believed that cortisol might play a role, however, as they removed the adrenal gland from the mice so that they couldn't produce cortisol-like hormones, their hair still turned gray under stress.
After systematically eliminating different possibilities, researchers honed in on the sympathetic nerve system, which is responsible for the body's fight-or-flight response.
Sympathetic nerves branch out into each hair follicle on the skin. The researchers found that stress causes these nerves to release the chemical norepinephrine, which gets taken up by nearby pigment-regenerating stem cells.
In a report released by Harvard's website, Hsu said: "When we started to study this, I expected that stress was bad for the body, but the detrimental impact of stress that we discovered was beyond what I imagined. After just a few days, all of the pigment-regenerating stem cells were lost. Once they're gone, you can't regenerate pigment anymore. The damage is permanent".
