The role of genetics in determining hair colour

It's common knowledge that our hair colour, among other features, are genetically inherited from our parents. However, do you know why, how and that there's more complex processes involved?

Leading hair transplant specialist Dr Nilofer Farjo goes into expert detail about the role that genetics play in determining hair colour.

How is genetics linked to hair colour?

The science of hair genetics still isn't completely understood. While we know many things about it, including how hair colour is determined entirely by your parents' genetic code, the question of hair colour is still an interesting one.

Do you remember learning about 'dominant' and 'submissive' genes in secondary school lessons, and how they control things like our eye and hair colour? Everyone has a pair of copies of each of their mother's and father's genes; one copy from their mother and one from their father. If the genes that relate to hair colour are both the same; for example, they both point to having brown hair, your hair will most likely be brown. If the copies are different to one another, then the dominant gene will determine the colour. We know that brown hair genes dominate over blonde, red and other hair colours. This means that blonde or red hair is only possible by having two matching recessive genes. 

What hair colour is the most common?

Global statistics show that black is the most common hair colour, followed by brown. Black and brown hair strands are usually thicker, as well as darker, than blonde hair. Furthermore, black hair is thicker than brown.

It's much less common to have blonde hair, and even less so to be a redhead. Red hair accounts for around one per cent of the global population and is most commonly found in the UK, with prevalence in Scotland reaching as high as 13 per cent of the population. As many as 40 per cent of Scots are believed to carry the recessive red hair gene.

What gives our hair its colour?

When we start to consider melanocytes, which actually gives our hair colour, things start to get a bit more complex. They make melanin, which is the pigment that is responsible for our skin colour as well as hair. It colours our hair at the root, using a combination of colours that are unique to you.  

In comparison to dominant and recessive genes, melanocytes are much more complicated. For example, siblings might both have brown hair but in differing shades. This is explained by the fact that melanocytes rely on a host of genes working together to produce a mixture of colours.

How is hair colour retained?

The key to retaining hair colour is melanin. Hormone changes as we get older impact the way it is produced. This explains why our hair often changes colour as we age, and most people, especially with blonde hair, will find how their hair gets darker as they get older.

Furthermore, melanocytes can start dying with age. This creates grey hair because the strand no longer has melanin pigmentation.

Can any other non-genetic factors impact hair colour?

Apart from dye, which is artificial, there are few other natural things that can impact hair colour. This includes:

• Sun exposure - Referred to as photobleaching, this is when UV light exposure brightens hair.

• Stress - There's evidence stating how excessive stress can prematurely cause death of the melanocytes, causing sudden hair greying.

• Medical conditions, which include albinism, vitiligo and malnutrition.

• There’s evidence that heavy smokers lose their melanocytes and go grey younger than non-smokers.

The Farjo team has undertaken extensive research into hair and hair loss. You can read our published work on the Farjo Hair Institute website, or get in touch with us.

If you're looking for expert hair and hair loss assistance, arrange an appointment with Dr Farjo via her Top Doctors profile.