The science behind hair colour

One of the fascinating things about the human species is that while we can all relate to one another on some level, each of us is unique in our genetic makeup, meaning that none of us look even remotely the same. This genetic makeup determines everything from the colour of our eyes and hair, to our skin tone, body build, growth rate and even personality.

Our hair colour is determined by how much of a pigment called melanin we have in the hair’s structure. There are many types of melanin, but the main two are eumelanin and pheomelanin. The higher the concentration of eumelanin the hair has, the darker it will be. Blonde hair, then, has the lowest amount of eumelanin in it. Pheomelanin, on the other hand, is what causes hair to be ginger. The higher the concentration of pheomelanin, the redder hair will be.

It is our genes that determine the type and amount of melanin in our hair. We don’t actually know much about most of them, but the gene that has been studied the most behind the scientific scenes is one called MC1R. This gene provides instructions for a protein called the melanocortin 1 receptor to be produced, which has a big part in the production of melanin.

So, how does the MC1R gene actually affect hair colour? Most people have two copies of the gene- and therefore more melanin will be produced, following the above structure. This means that those with the MC1R gene have dark brown or black hair, which is most common around the world (it is estimated a good 90% of people have two copies of the gene).

The people with only one copy of the gene have light brown or blonde hair, as a result of less melanocortin 1 receptors being produced, which in turn leads to a lower production of melanin. It is common in people with one copy of MC1R to have a higher pheomelanin production, which is why blonde and ginger hair is often genetically linked.

Hair colour can sometimes change over time, so if you were born with much lighter or darker hair, it is possibly for it to naturally lighten or darken as you age. Scientists believe that the reason behind this might have something to do with certain melanin-linked proteins only being switched on later on in life, potentially in response to puberty. This is why some blonde-haired children end up with much darker hair as adults.

Of course, hair colour then changes again later on in life. Nearly all hair will naturally turn grey or white at any age, with some people even finding their first grey hairs in high school, although it is more common to happen in our thirties or forties. Hair does not actually “turn” grey- instead, it loses pigments over time, which means that it contains less melanin, which is what gives hair its unique colour.

Again, how early our hair goes grey is generally determined by our genes. It is usual for grandads, dads and sons to all go grey at around the same stage in life. It is possible, of course, to dye your grey hair to another colour of your choice, but that is no longer the preferred option nowadays. More and more people are embracing their grey hair, with the shade having so much appeal that even younger people are dying their hair in shades of “silver” as a trend.

As for the idea that hair can change colour- notably, go grey- with stress? It’s all a big myth. Grey hair relates to having a lower melanin production, which is not affected by stress in the slightest. One study has found that long-term stress (not just the type you feel when you burn your dinner) may be linked to hormone production, including those in the hair, which may lead to a dip in melanin production. However, no clear link has been found between stress and grey hair as of yet. So all those times your parents blamed you for making your hair go grey… you can now explain to them exactly why that isn’t true!

Laura Shallcross