You are probably familiar with the expression ‘get grey hair.’ It originated in the 19th century and was built around the observation that some people who had suffered a major emotional shock saw their hair suddenly turn grey. In fact, it happens that a period of stress, either sudden or extended over time, can cause hair or a beard to turn grey. That's why Barack Obama ended his 8 years in office with a whole lot more grey hair. What is the cause of this phenomenon? Not the same as hair affected by old ageDiscreetly or in large tufts, hair can sometimes turn grey without warning. Why is this? Hair follicles have a stock of melanin, the natural hair colouring agent, and when the stock is completely depleted, hair grows without colour, making it appear grey. A gene is also believed to be responsible for grey hair.But in the case of stress, what happens in our body from a scientific point of view? After all, the process is not exactly the same as in old age. Several studies have been carried out on the subject, and Harvard researchers seem to have found the answer.The predominant role of norepinephrineThey studied the effects of autoimmune attacks on the follicle, using tests on mice. When we're stressed, our bodies produce norepinephrine, also known as noradrenaline, a chemical compound that acts as a neurotransmitter. To put it simply, it acts as a hormone. It is also a precursor of adrenaline, which is released into the bloodstream when stress or physical effort is at its peak. All this with one aim, to make the body react: increase in heart rate, dilated pupils, slowing down of intestinal activity...The release of norepinephrine thus has an effect on mood, sleep, and emotional control... However, scientists at Harvard University are suggesting that what causes accelerated greying of hair when under stress is this molecule.In addition to all the functions already mentioned, it is also believed to activate the melanocyte stem cells, the pigment stock of the hair, in response to this shock. This would cause it to run out and when it is completely gone, the hair then becomes irreversibly grey. So to avoid this phenomenon, try to establish an anti-stress routine in your daily life.What about patches of grey hair?But what about when hair gradually goes grey in patches? In this case, this is not necessarily caused by stress... but by vitiligo. This is a chronic skin disease, also known as leukoderma or achromia. In this case, the body is strewn with depigmented spots, particularly on the feet, hands, and face. However, the pathology is completely painless. And there you have it, now you know everything there is to know about grey hair!