Drew Barrymore

Mean Girls was right when it posited that hair can be full of secrets. Scientists can determine person’s eating habits, body mass index, and sex from a single strand, proving that a hairdo can do more than make or break an iconic look. But while experts can tell what drugs a person has done through hair analysis, it’s been a lot harder to discern something far more basic — why our hair color is the way it is. But thanks to a new study that analyzed huge genetic data sets from 23andMe, our roots have just become a lot more obvious.

On Monday, an international team of scientists announced that the measly 12 genes previously attributed to hair color were a huge understatement: They write in Nature Genetics that there are actually 124 genes that play a major role in determining hair color variation. Filling in this genetic knowledge gap gives us more than just explaining why we look the way we do: The study authors are hopeful that this discovering can advance our understanding of conditions linked to pigmentation, like skin cancer, and be push forward forensic science technology.

“Besides substantially increasing our understanding of human pigmentation genetics in general, finding these new hair color genes is also important for further increasing the accuracy of hair color predictions from DNA traces in future forensic applications, which can help to find unknown perpetrators of crime,” co-lead author Manfred Kayser, Ph.D., of Erasmus MC University Medical Center Rotterdam, explained in a statement released Monday.

Liv Tyler, hair
124 genes play a role in determining hair color variation.

This study is the largest genetic study on pigmentation to ever be conducted and used a massive amount of data supplied by 23andMe Inc., the International Visible Trait Genetics Consortium, and the UK Biobank. Kayser and his co-authors analyzed DNA data belonging to approximately 300,000 people of European descent who either had black, blond, dark brown, light brown, or red hair. While genetic information is stored at several million locations across the human genome, there are precisely 124 genes that are involved in the development of hair color — 100 of which were not previously known to affect pigmentation.

In this particular population of candidates, there was a prevalence of lighter hair colors among women, suggesting there might be a link between sex and hair color. The link between hair color and genes was so robust that the researchers could use a person’s genetic data to accurately predict who had black or red hair with high accuracy (they had a harder time doing the same with blonde or brown hair, though).

Natural pigmentation, which affects the color of skin and hair, comes down to the two types of melanin a person’s cells produce. Studies on twins have shown that a person’s genetics account for 97 percent of color variation, and we can see this in populations of people. It’s thought that early humans evolved to have darker skin to protect against high ultraviolet radiation, and that Europeans and Asians evolved to have lighter skin as they moved towards northern latitudes.

Your hair color may connect you to your ancestral past, but it also affects your present-day susceptibility to diseases like cancer. Because pigment genes are linked to your chances of developing Crohn’s and other forms of bowel disease, the scientists behind this new study are hopeful this trove of data can be used in future medical studies.

“While the genetics of hair color is an interesting problem in itself,” co-author and 23andMe scientist David Hinds, Ph.D., explained in a statement, “we hope that better understanding of the biology of melanin pigmentation will be applicable to studies of diseases that interact with pigmentation, such as skin cancer or vitiligo.”