Red Hair: it’s in your genes 

A quick question: what do Prince Harry, Ed Sheeran, Jessica Chastain and Julianne Moore have in common? That’s right, their hair color: they are all natural redheads! 

Everyone is aware of red hair, but overall it is not that common as it is estimated that just 1-2% of the global population has red hair. However, there are geographical differences and red hair is more common in Northern Europe, particularly in Scotland and Ireland.

What causes this small percentage of people to have red hair? It might not surprise you to hear that the answer is in your genes. 

Eumelanin and pheomelanin: a natural paint palette  

Melanin is your body’s natural pigment. It is made by special cells called melanocytes and the amount of it you have influences your skin, hair and eye color. If you have a lot of melanin, your hair, skin and eyes will be darker in color than someone who produces less. In turn, the amount of melanin you produce is influenced by your genes. This means that you are born with the tendency to produce more or less melanin.

There are two types of melanin involved in pigmentation: eumelanin and pheomelanin. Eumelanin is responsible for dark colors and occurs in brown and black forms and pheomelanin is responsible for pink areas of the skin. The amount of each type in combination determines the hair color. For example, if you have a large amount of eumelanin then you will have black hair. If you have only a very small amount of brown eumelanin then you will have blond hair, while a mixture of pheomelanin and low levels of eumelanin will lead to strawberry blond hair [1]. Redheads have more pheomelanin than eumelanin, due to either increased pheomelanin production or reduced eumelanin production [2].  

You have probably noticed that people with red hair often have pale or fair skin and freckles. This is also influenced by the amount of melanin. 

Redheads have more pheomelanin 

Redheads produce more pheomelanin due to genetic changes (called variants) in the MC1R gene found on chromosome 16. This gene provides the code for a protein called melanocortin 1 receptor that is located on melanocytes and is responsible for the type of melanin produced. When the receptor is activated or turned on, melanocytes produce eumelanin. In contrast, if the receptor is not activated the melanocytes produce pheomelanin. Variations in the MC1R gene are responsible for this deactivation [3]. 

Although MC1R gene sequence variants have been found in over 80% of redheads and/or people with fair skin that does not tan [2], this may not be the complete story. A 2018 study [4] of more than 343,000 UK Biobank participants found that MC1R accounts for only 73% of the genetic heritability of hair color. The authors reported that although 93% of people with red hair carry two MC1R variants, this corresponds to only 15% of people with two MC1R variants and that in fact, two MC1R variants are most often associated with blonde or light brown hair. The authors went on to identify eight additional variants associated with red hair including a variant in an intron of RALY that influences the expression of ASIP in the skin (expression controls whether a gene is turned on or off). An earlier study in Northern Europeans previously identified the role of a variant in ASIP in red hair [5] and the authors of the 2018 study surmised that variants that increase ASIP expression in skin or hair follicles cause increased pheomelanin in melanocytes [4]. They also found evidence of epistatic interactions (these are interactions between two or more genes which modify the effect of one gene) as some genes control when MC1R is switched on or off [6]. This suggests that the genetics of red hair is more complicated than it first appears. 

It is also interesting to note that the authors of the 2018 study found a variant in HERC2 associated with a decreased probability of red hair [4]. 

Shades of red 

Red hair comes in many shades of red, from copper and bright orange to strawberry blond. This is partly due to the specific combination of eumelanin and pheomelanin but is probably also influenced by the interactions of other genes, such as ASIP, that determine hair color. Many genes are known to be involved in hair color [3] – the 2018 UK Biobank study reported genetic variation in 200 genes associated with blond or brown hair [4, 6] – but more research is required to determine specific details. 

Inheritance of red hair 

As mentioned above, the amount of melanin you produce is influenced by your genes, and as a result, hair color can be considered a genetically determined characteristic or trait.  

Red hair runs in families, but non-redhead parents can also have a red haired child. So how exactly does genetics influence hair color?  

MC1R is a recessive gene. This means that two copies (one inherited from each parent) are required for the trait to be observed. In this case, two copies of the variant are required for the child to be a redhead. In other words, if only one copy of the variant is inherited, the trait will not be seen, i.e., the child will not have red hair, but they will be a carrier and able to pass the variant on to the next generation. Therefore, two carriers (non-redheads) will be able to have a red-haired child. This is called autosomal recessive inheritance and understanding it allows us to predict the chances of having a child with red hair. 

Redheads have two copies of the variant; therefore, if both parents have red hair then their offspring will also have red hair. If one parent has red hair and the other is a carrier, there is a 50% chance that a child will inherit red hair, and two non-redheads carrying the recessive gene have a 25% chance of having a child with red hair.  

Health risks for people with red hair

As well as their standout hair color, redheads seem to be more likely as a group to develop certain health conditions and have certain health risks. These include:

• Increased skin cancer risk
• Altered sensitivity to pain
• Increased risk of Parkinson’s disease
• Increased risk of endometriosis

Read more about health risks for people with red hair here.

Conclusion 

Although the inheritance of red hair seems simple enough to understand, the genetics behind it are complicated. Studies have shown that multiple genes are involved in pigment production and hair color and that genetic interactions are also important. Red hair comes in many shades of red from copper to strawberry blond and maybe in time, our understanding of genetics will enable us to determine the combination of factors responsible for each hue.  

References