The role of stress in turning hair gray appears not to be science fiction or societal myth. The basis of long-used anecdotes about people’s locks losing their color, stress plays a more pivotal role in this process than previously thought, according to new research.
Scientists know that other factors—including genetic mutations, immune attacks, and natural aging—can lead to loss of hair color, but a lack of scientific evidence linking stress to graying hair has left many experts scratching their heads. Recently, however, researchers at Harvard University, including Ya-Chieh Hsu, Ph.D., an associate professor and 2017 Pew biomedical scholar, published findings in Nature that detail how stress can cause damage to the pigment-producing stem cells in hair follicles.
When it started this work, the Harvard team speculated that stress evokes an immune attack on melanocyte stem cells, which transform into melanin-producing cells to give hair its color. After injecting mice with a compound similar to capsaicin—the heat-inducing component of chili peppers—to produce a stress reaction, researchers observed that the mice’s fur turned a salt-and-pepper color, and after five days, lost its pigment completely. However, their experiments revealed that this wasn’t because of an immune system attack, because even mice without compromised immune systems ended up with gray fur.
Hsu’s lab next looked at the stress hormone cortisol as a possible offender. Surprisingly, researchers found that the mice’s fur still turned gray in response to stress even when their adrenal glands were removed to block cortisol production.
After ruling out other factors, the team decided to investigate a new suspect: the sympathetic nervous system, which directs the body’s fight-or-flight response. Researchers found that chemicals released from sympathetic nerves under stress can cause permanent damage to melanocyte stem cells. During periods of stress, the mice’s sympathetic nervous systems released norepinephrine—the chemical responsible for muscle contraction—which was then taken up by melanocyte stem cells in each hair follicle.
This triggered the melanocyte stem cells to convert into pigment-producing melanocytes, causing a limited reservoir of stem cells to rapidly deplete. And because there are no stem cells to replenish new melanocytes, this ultimately causes hair to turn gray.
Hsu’s team demonstrated that acute stress affects the entire melanocyte stem cell population not only in mice but also in humans. Researchers observed the rapid generation of human melanocyte stem cells in petri dishes, hinting that people experience a similar hair graying process.
Although there is currently no treatment available to stop or reverse hair graying, these findings may help scientists better understand how stress affects the body and ultimately how to combat its detrimental effects. Hsu said that after laying this critical groundwork, she hopes to take this research further to analyze whether stress causes people to age faster.
Kara Coleman directs The Pew Charitable Trusts’ biomedical programs, including the biomedical scholars, Pew-Stewart Scholars for Cancer Research, and Latin American fellows programs, and Jennifer Villa is a principal associate supporting the programs.