Why Hair Grows Grey is Not A Puzzle Anymore

Scientists link up the nervous system and stem cells for regenerating pigment.

Why Hair Grows Grey is Not A Puzzle Anymore
Grey Hair
Why Hair Grows Grey is Not A Puzzle Anymore

Why Hair Grows Grey is Not A Puzzle Anymore.


Our hair turns grey when we are in excessive stress. From history, we come to know about many instances of hair color transformation. During the French Revolution, Marie Antoinette lost her hair color overnight after being captured. John McCain is a prisoner of the Vietnam War. The result of the severe injuries in the prison was visible in his hair as they turned grey.

Many anecdotes from history connect hair color loss with stressful experiences. The exact process that how the hair turns gray is an ever-peeping question in our mind. The scientists from Harvard University take this question as a subject of research for the first time. Stress activates many of the nerves. These nerves are part of the fight-or-flight response. Stress permanently damages to pigment-regenerating stem cells. The stem cells are essential in hair follicles.

The results of the study are published in Nature paving ways to other researchers to find out how stress impacts our body. 

Ya-Chieh Hsu is the senior author of the study. He is both the Alvin and Esta Star Associate Professor of Stem Cell and Regenerative Biology at Harvard. He says, "Everyone has an anecdote to share about how stress affects their body, particularly in their skin and hair -- the only tissues we can see from the outside. We wanted to understand if this connection is true, and if so, how stress leads to changes in diverse tissues. Hair pigmentation is such an accessible and tractable system to start with and besides, we were genuinely curious to see if stress indeed leads to hair graying. "


Eliminating other possibilities

Stress alone has the ability to affect the whole body. So, scientists need to determine which body system is particularly responsible for turning hair color gery. First of all, the researchers hypothesized an immune attack caused by stress. It attempts the pigment-producing cells. On research on the mice, they found that their hair also grows grey for the lack of immune cells. The team also

Hsu said, "Stress always elevates levels of the hormone cortisol in the body, so we thought that cortisol might play a role. But surprisingly, when we removed the adrenal gland from the mice so that they couldn't produce cortisol-like hormones, their hair still turned gray under stress."

The team had many possibilities but they did not take all of them. Among the possibilities, they took the sympathetic nerve system especially. This system is essential for the body's fight-or-flight response.   

The branches of the sympathetic nerves end in hair follicles on the skin. When stress occurs, the nerves release a chemical named norepinephrine. The researchers found that this chemical affects the pigment-regenerating stem cells nearby.



Long-lasting damage

There is a certain amount of stem cells in our hair follicle acting as a reservoir of pigment-producing cells. Pigment-producing cells color the hair. At the time of hair generating, some stem cells change into pigment-producing cells.

According to the researchers, sympathetic nerves release the norepinephrine that activates the stem cells excessively. The stem cells all convert into pigment-producing cells, prematurely depleting the reservoir.

Hsu says, "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."

Another lead author of the study is Bing Zhang, a postdoctoral fellow. He says, "Acute stress, particularly the fight-or-flight response, has been traditionally viewed to be beneficial for an animal's survival. But in this case, acute stress causes permanent depletion of stem cells." 



Fundamental questions and answers

The team started to determine the relationship between stress and hair greying by observing the whole-body response. After that, they focused on individual organ systems and then cell-to-cell interaction. Finally, they took consideration of molecular dynamics. All these need a great effort and a wide range of methods. Even they needed to manipulate organs, nerves, and cell receptors.

Zhang says, "To go from the highest level to the smallest detail, we collaborated with many scientists across a wide range of disciplines, using a combination of different approaches to solve a very fundamental biological question."

Isaac Chiu also played a major role in the research paper. He is an assistant professor of immunology at Harvard Medical School. He says, "We know that peripheral neurons powerfully regulate organ function, blood vessels, and immunity, but less is known about how they regulate stem cells. With this study, we now know that neurons can control stem cells and their function, and can explain how they interact at the cellular and molecular level to link stress with hair graying."

So far, we know that stress affects our hair color. The study hints on other organs and tissues can be the victim of stress’ effects. Other researchers will come forward to illuminate stress’s effects on us by analyzing the results of the study.

Hsu says, "By understanding precisely how stress affects stem cells that regenerate pigment, we've laid the groundwork for understanding how stress affects other tissues and organs in the body. Understanding how our tissues change under stress is the first critical step towards eventual treatment that can halt or revert the detrimental impact of stress. We still have a lot to learn in this area."