There are many people who look at their childhood photos and see almost Nordic blonde hair, but when they look in the mirror and see dark brown hair, they wonder… what happened? This story is not a rare occurrence, but data suggests that more than 70% of children who are born blonde within two or three years have brown hair before they reach puberty. Although this statistic comes out of a study of Polish children who are more prone to be born blonde.
What’s behind. To understand why hair turns black, one must look at the root of the hair follicle, which is specifically the melanocytic cells. They are really important, because they act as pigment factories of the human body, and especially two that interest us a lot in this field:
- Eumelanin: Responsible for dark brown and black tones.
- Pheomelanin: Gives reddish and yellowish nuances.
final color. It depends on the correct ratio between these two pigments, and this is why in blonde children, the melanocytes of the follicle secrete a greater relative amount of pheomelanin or, simply, produce very low levels of normal eumelanin. However, this production changes over time because we are not talking about a fixed process, much less specific.
Regulations. The master switch controlling this ratio is the melanocortin 1 receptor, also known as MC1R. This is quite important, because when alpha melanocyte-stimulating hormone activates it, the cell is forced to change the production line it is carrying, the ‘production’ going from lighter pheomelanin to darker eumelanin.
This process is well known in the skin, where DNA damage caused by UV radiation triggers the release of these hormones to create the characteristic tan we all want. In the hair follicle, on the other hand, the triggers for darkening do not come from the sun, but are endogenous and seem to be dictated by an internal biological clock.
The turning point Historically, it was thought that the darkening of hair was due to the hormonal cascade that we experience during puberty and occurs between the ages of 10 and 13. But recent data suggest that hair follicle darkening can be detected as early as age 6, indicating that the transition to brown begins much earlier than puberty. The problem is that we don’t know exactly why this happens in some children and not in others.
adults Once we get past childhood, our hair color can change, as there are times like pregnancy where the peak of estrogen and progesterone can darken our hair, although there are many doubts behind this.
Forensic. All of this biological ambiguity translates into a very real problem for forensic genetics: When investigators extract DNA from crime scenes and feed the data into predictive models, algorithms often predict a blond phenotype for suspects who, as adults, are clearly brown.
And at this point we can only read the genotype we had from childhood, without all the changes that occur throughout life with epigenetics. As we once again see how our future is not only ‘condemned’ to genetics, but strongly intervened by what happens around us.
Picture | Bashar Ketaj
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