Hair characteristics

Note: We have made every effort to gather research spanning as many and as diverse populations as possible, but there is still work to be done to make reports more inclusive. We will continue to periodically review and update this report as more research becomes available.

Introduction

Studies investigating hair colour have found this trait to be between 73%-99% genetically inherited [1] Jump to reference section: [1] , whilst hair curliness is considered to be between 85% to 95% genetically inherited [2] Jump to reference section: [2] . Numerous studies have identified a host of genes that carry the instructions for the colour, texture and even thickness of our hair. Here we identify genetic variants that you might carry that have been shown to affect these hair characteristics.

Light, dark or red?

Hair colour varies due to differences in the  amount of a pigment called melanin that we all have in our hair. There are two types of melanin that, depending on the relative abundance of each, decide our hair colour. These are known as eumelanin and pheomelanin. The greater amount of eumelanin present in your hair, the more dark haired you’ll appear, with even higher levels resulting in black hair. Meanwhile, a lack of eumelanin results in blonde hair, while higher levels of pheomelanin result in red hair. 

Melanin production is controlled by a number of genes across many different chromosomes. However, a particular variant on the KITLG gene has been shown to have an effect on one’s hair colour. The KITLG gene is involved in numerous processes throughout the body. One of these is the production of melanin. Researchers have found that those with a ‘C’ variant at the rs12821256 site of the gene are more likely to have blonde hair [3] Jump to reference section: [3] .

Similarly, The MC1R gene is also known to regulate production of melanin. The MC1R gene carries the instructions for a protein that signals your melanin producing cells, known as melanocytes, to start producing eumelanin. Otherwise, the default state of melanocytes is to produce pheomelanin. 

Interestingly, a mutation on the MC1R gene is strongly associated with having red hair.  Those with a ‘T’ variant at rs1805007 are around 10x more likely to exhibit red hair. This mutation likely contributes to stopping MC1R from sending the instructions to produce eumelanin, and instead is likely telling the cell to continue to produce more pheomelanin instead. However, it should be noted that up to 30 variants on MC1R have all been shown to play a role in making one’s hair red, and that it’s possible to have one or two of these variants and still have blonde or dark hair [4] Jump to reference section: [4] .

Straight or curly?

Differences in hair texture are thought to be dependent on the shape of the bottom of our hair follicles, as this determines how a protein called keratin continues to construct the follicle as it grows. The gene TCHHL1 carries instructions for a protein within the ‘Trichohyalin’ family. This protein is known to interact with keratin, and is predominantly expressed in hair roots [5] Jump to reference section: [5] . Interestingly, a variant of the gene TCHHL1 is associated with decreased curliness. Those with an ‘A’ allele at rs17646946 have been shown to have a reduction in hair curliness compared to those without [6] Jump to reference section: [6] .

The TCHHL1 gene, however, appears to play a role in hair curliness in a way that's mainly limited to European populations - though it has also been implicated in Latin America [7] Jump to reference section: [7] . Scientists have gone on to discover that different genes, in different populations, are more likely to cause changes in hair curliness in those groups. Research has established that the ‘EDAR’ gene is implicated in hair curliness variation in East Asian populations. EDAR is involved in numerous biological processes, one of which is assisting in the production of ectodermal cells where skin, hair, teeth and nails are produced from. Scientists have established that - for people with East Asian ancestry - a ‘C’ variant at rs3827760 on the EDAR gene makes you twice as likely to have straight hair [8] Jump to reference section: [8] .

Thick or thin?

For a long time the genetics behind hair follicle thickness were little understood. Not to be confused with density (the amount of follicles in a given area), thickness refers to the average circumference of individual hair follicles. For a while it was known that East Asian populations often had thicker hair than their European neighbours. This formed the basis for the first studies investigating the genetics of hair thickness. Scientists, by looking specifically at East Asian populations and comparing their hair thickness and genetic variants, were able to locate a particular variant that was strongly associated with hair thickness. They established that the same ‘G’ variant at rs3827760 on the EDAR gene associated with straight hair, was also significantly associated with thicker hair too[9] Jump to reference section: [9] . 

What does this mean for me?

Whilst the characteristics of our hair are very much genetically inherited, it’s important to understand that the variants outlined in this report are not exhaustive, and there are many other variants also playing a role. You might, for example,  find yourself reading this report and seeing you have variants for blonde hair, yet you might actually have brown hair. This is because there are many genes across your whole genome affecting your hair characteristics, all playing a complex and interdependent role in making you, you.