Sometimes an evolutionary response does us a disservice.
Don’t stress. It will only make things worse.
RUNSTUDIO
By Amelia Nichele
Science can’t yet stop stress turning your hair grey, but it can at least explain how it happens – if that’s any consolation.
Stress activates nerves that are part of the fight-or-flight response, causing permanent damage to pigment regenerating stem cells in hair follicles, according to a team from Harvard University in the US.
"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," says senior author Ya-Chieh Hsu. "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 greying."
The work with mice – described in a paper in the journal Nature – wasn’t straightforward.
At first, the researchers suspected that stress triggers an immune attack on pigment-producing cells. This was discounted, however, when mice without immune cells still showed greying hair.
A series of dead-ends eventually led them to the sympathetic nerve system.
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Sympathetic nerves branch out into each hair follicle. When under stress, they release the chemical norepinephrine, which is taken up by nearby pigment-regenerating stem cells.
The norepinephrine causes the stem cells to activate excessively, with all the cells converting into pigment-producing cells.
"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,” Hsu says.
The finding highlights the negative side effects of an otherwise protective evolutionary response, the researchers say.
"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," says lead author Bing Zhang.
Hsu, Zhang and colleagues suggest their research is a step towards developing ways to block the effects of stress in the future.
“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,” Hsu says.
“Understanding how 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."
