London: It was long thought to be an old wives’ tale. But stress really does make your hair go grey – and once it’s changed color it won’t ever go back, scientists say. A Harvard University study on mice found the culprit was norepinephrine, a hormone released when the body goes into ‘fight-or-flight’ mode.
Under immense stress, norepinephrine is released into the bloodstream where it ramps up heart rate and prepares the body to react to a threat. But it appears to damage melanocyte stem cells (MSCs), pigment-producing skin cells that give hair its color.
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People typically start to go grey in their 30s and have half a head of grey hair by the time they are 50. Premature greying, as early as teenage years, is believed to be caused largely by genetics. But whether or not stress can cause hair to change color has been fiercely debated by scientists for years.
The senior author of the latest study, published in Nature, said most people have an anecdote of how stress caused a reaction in their body. ‘Particularly in their skin and hair – the only tissues we can see from the outside,’ Dr Ya-Chieh Hsu, professor of stem cell and regenerative biology at Harvard, said.
‘We wanted to understand if this connection is true, and if so, how stress leads to changes in diverse tissues.’ It’s previously been shown that hormones produced in response to stress can deplete the stem cells that color hair. But the researchers wanted to determine which hormones they are – and where they come from.
Harvard scientists honed in on the sympathetic nerve system, which is partially responsible for the body’s fight-or-flight response. It directs the body how to respond to stressful or dangerous situations, boosting heart rate and sending blood to the muscles, for example.
Sympathetic nerves branch out into skin cells – including hair follicles – to collect information on the environment. A side effect of the response is that changing the levels of hormones may warp the function of cells. Hair follicles contain certain melanocyte stem cells, which color the skin and hair with a pigment called melanin.
The researchers found that stress causes sympathetic nerves to release the chemical norepinephrine into the blood. Norepinephrine, a neurotransmitter produced by the brain in both minor and chronic stress situations, makes the body more alert and ready to fight stress.
But it also causes the stem cells in hair follicles to activate excessively, the study found. The stem cells go through a process called proliferation and differentiation, where they switch into specialized cells.
In other words, their role changes and they move away to other parts of the body, leaving the hair follicles depleted. Mice exposed to physical or psychological stress showed a reduction in numbers of melanocyte stem cells within days. Their hair greyed at a faster rate.
Within 24 hours of being injected with norepinephrine, the mice had lost about 50 percent of their stem cells to proliferation. When the scientists blocked proliferation of stem cells, it prevented the loss of melanocyte stem cells and hair greying in the mice.
Dr. Hsu said: ‘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.’ The study shows greying is driven by activation of the sympathetic nervous system, contrary to previous theories.