In the middle of a bout of stress, you look in the mirror, only to find a strand of white lightning running through your hair. Is it a coincidence, or does stress actually make us go grey?

For the first time, Harvard University scientists have discovered that stress activates nerves that are part of the body’s fight-or-flight response, which in turn cause permanent damage to pigment-regenerating stem cells in your hair follicles. Once the greys rock up, they’re here to stay. 

The study, published in the journal Nature, advances previous knowledge of how stress impacts the body and could even pave the way for solutions to prevent the effects of stress in future.

In the meantime, it’s yet more proof (if we needed it) that we all need to stress less.

What happened in the study?

Stress affects the whole body, so researchers firstly had to narrow down what body system was responsible for connecting stress to a change in hair colour.

The team first thought stress caused an immune attack on pigment-producing cells. However, when mice lacking immune cells still showed hair greying, researchers turned their attention to the stress hormone cortisol. Again, this was a dead end.

After eliminating different possibilities, researchers honed in on the sympathetic nerve system, which is responsible for the body’s fight-or-flight response. A discovery was made.

A nervous response

Sympathetic nerves branch out into each hair follicle on the skin. The researchers found that stress causes these nerves to release a chemical called norepinephrine.

In the hair follicle, certain stem cells act as a reservoir of pigment-producing cells. When hair regenerates, some of the stem cells convert into these pigment-producing cells that colour the hair.

Researchers found that norepinephrine causes the stem cells to activate excessively. The stem cells all convert into pigment-producing cells – but after just a few days, all these cells are lost, so there are no cells left that colour the hair.

“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,” said senior author Ya-Chieh Hsu, from Harvard. “Once they’re gone, you can’t regenerate pigment anymore. The damage is permanent.”

What does it all mean?

Stress has been traditionally viewed as beneficial for survival, but more studies are showing the negative impacts – from poor heart health to grey hairs. 

It’s thought the study’s findings may help illuminate the broader effects of stress on various organs and tissues. It could even pave the way for new studies that seek to modify or block the damaging effects of stress.

“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,” said Hsu. “We still have a lot to learn in this area.”