After years of going back and forth on the great gray debate – namely, whether grays are a product of stress or just a natural part of aging – we finally have a scientific answer. Evidence up to this point has been largely anecdotal, and probably the best example is former President Obama’s strands, which were deep black when he entered office in 2008. When he exited the White House in 2016, his hair was definitely more salt than pepper. Enter, Ya-Chieh Hsu, Ph.D., Faculty Member at the Harvard Stem Cell Institute and Associate Professor of Stem Cell and Regenerative Biology at Harvard University, who wanted to know what causes grays, once and for all – here’s what she found…
Ya-Chieh starts out by reminding us that stress is detrimental to our health – take a deep exhale as you’re reading this – and that there’s more then one type of stress (an idea that was central to her findings). For instance, the response your body produces when you’re anxious about school or work is very different than when you think someone is chasing you down the street — and how you react to each situation will have very different effects on your body. “Acute stress can have profound and detrimental effects on human health, and these effects could be particularly pronounced among those whose professions involve high levels of stress — emergency responders, healthcare workers, and veterans, among others. Emotional stress is only one type of response that can disrupt normal physiological function. Stressors such as illness, physical injuries and pain are potent and damaging,” she describes.
Different stress produces different responses
Despite this understanding, how different types of stressors damage the body has gone relatively unexplored. Ya-Chieh realized that hair color was a great place to start tracking the effects of stress, “if only because hair is so visible and easily accessible,” say explains. “And because stem cells are crucial for tissue regeneration and healing, we looked closely at the stem cells in skin and hair to investigate the impact of stress on stem cells. Mouse studies helped us understand how stress affects the specific stem cells in hair follicles that are responsible for making pigment cells.”
Ya-Chieh originally hypothesized that stress would lead to an immune attack on cells that produce pigment. This wasn’t the case, however. She then thought that cortisol (everyone’s favorite stress hormone) would be responsible for turning dark hair, gray, but this was also proved wrong. Finally, Ya-Chieh and her team turned their attention on the sympathetic nervous system, which is more commonly known for triggering a “fight or flight” response. Though the system is viewed as beneficial, and its effects have been thought of as transient, it can cause irreversible damage to hair pigment.
“Under acute stress, the entire population of these melanocyte stem cells is activated. They all turn into pigment-producing cells – every single one of them. Some go to the hair root, others seem to wander off into the skin. None are left in the self-renewing state,” she explains.
“That’s because under stress, when our sympathetic nerve becomes highly activated, it triggers the fight-or-flight response through a neurotransmitter called norepinephrine, or noradrenaline. Sympathetic nerves wrap around each hair follicle, so the norepinephrine they release has an impact on the stem cell population quite quickly and can destroy it permanently. Without melanocyte stem cells, pigment cells cannot be regenerated,” she continues, breaking down this pigment-killing process.
While this experiment has played out in mice and not humans, the team assumes that the results will translate the same. Once firm proof that grays are triggered by the sympathetic nervous system is established, researchers can begin to block the effects (!).
Although we’re optimistic for a gray-less future, this isn’t the only reason hair fades. The aging process, genetic mutations and immune attacks all contribute to fading hair pigment — but now we also know the link between very acute stress and graying.