Oh dear, is that a grey hair you spy in the mirror?
- Did you know that overall, men have more grey hairs than women?
- And that for three quarters of people in the 45 to 65 year old age bracket, one quarter of their total hair count is grey.
- Also, by the time half of us hit 50, we’ll have lost colour in 50% of our hair – you could call this the 50/50/50 rule!
- Many of us start noticing the odd grey hair sneaking in around 30. They usually appear first at the temples before spreading.
But have you ever wondered just how, or why, we go grey?
In horses the popular grey coat colour is caused by a genetic mutation in a gene called the STX17 gene. This gene is thought to be involved in regulating the melanocyte stem cells and melanocytes that are needed to produce hair and skin pigmentation respectively. The mutation appears to cause an early loss of the melanocyte stem cells within the hair shaft that produce coat pigment whilst upregulating, or overproducing, skin pigmentation melanocytes. The result is a foal that is born a ‘base colour’ but prematurely turns grey. The foal is also generally born with much darker skin than a non-grey foal of the same base colour due to the hyperpigmentation caused by overproduction of skin pigmentation melanocytes. Grey is also a dominant gene, which means that if it’s carried it is ALWAYS expressed.
Whilst grey in horses may be popular – who doesn’t love the team of Windsor Greys that pull the carriages of the British Royal Family – grey hair in humans in not nearly so welcome! Many people go to a great deal of trouble to hide it. But unfortunately, as we can see by the statistics mentioned earlier, for many of us it isn’t a case of if, but when.
Fortunately the reason people go grey is not nearly so dramatic as it is in horses. There are no genetic mutations involved or hyperpigmentation. However, the genetic structures that manufacture pigment are similar across all species of mammals – we all have melanocytes in our hair follicle bulbs, and our skin, that produce the pigment (melanin) we see in skin and hair. The melanin is stored in vesicles, or containers, called melanosomes. Melanin in mammals only comes in 2 colours – black and red. Regardless of species. ‘Abnormal’ colours like light blonde are the result of genetic mutations that modify the way melanosomes manufacture melanin (or artificial hair dyes!) The range of shades within the base black (brown to black) and red (yellow to red) pigments is caused by variations in the ratio of black and red pigments.
And also interestingly, many of the mutations that affect hair pigment occur in similar genes and cause similar effects across species too. The OCR2 mutation for example, one of the albinism mutations in humans that produces blue eyes, very fair skin and almost pure white hair, has a similar mutation in other species and it modifies pigment production in very similar ways. In mice it’s called underwhite and in horses it’s called cream.
But back to grey hairs in humans.…
We mentioned earlier that melanocytes in the bulb of our hair follicles are responsible for manufacturing the pigment that colours our hair. As our hair follicles cycle through their anagen, catagen and telogen phases, the bulb is reabsorbed and recreated every time the follicle produces a new hair. This means that melanocytes in the bulb are also damaged and die off. They’re replaced by melanocyte stem cells from the stem cell reservoir located in the permanent top section of the hair shaft. However, eventually the reservoir runs out of melanocyte stem cells. This means pigment production in that hair follicle ceases and all future hairs produced by that follicle are grey. As not all hair follicles are in the same stage of growth at the same time, and not all hair follicles run out of melanocyte stem cells at the same rate, most of us go through salt and pepper stages before all our hair follicles eventually run out of melanocyte cells and we end up with pure white hair. There are also many people who never run out of melanocyte cells in their hair follicles. These are the lucky ones who still have coloured hair even at an advanced age!