Not everyone sees their hair go gray at the same time: for some it happens sooner, for others later, and for a lucky few it doesn’t happen at all. A question of genetics, but not only: experiences, illnesses, sorrows and stressful periods can also influence the speed with which hair turns grey. In recent years, various research has begun to clarify the mechanisms by which hair greys, bringing us closer to the day when it will be possible to return to having intensely colored hair like the one we exhibited as kids, without the need to resort to dyes or other cosmetic products. Let’s see where I am at.
The hair follicles
One of the fundamental pieces for understanding gray hair came in 2023 from a study published in Nature by a group of researchers from New York University. The research, conducted on mice, revealed a peculiar mechanism that compromises the correct functioning of the stem cells from which the melanocytes responsible for the production of the pigments that give color to our hair originate.
Unlike almost all other stem cells, which typically develop first into progenitor cells and then into mature differentiated cells, melanocyte stem cells possess the ability to travel cyclically back and forth along the developmental scale. In healthy hair follicles, these cells continuously move between different compartments to regenerate and transform into mature cells capable of producing pigment, and then return to de-differentiate within an area of the follicle called the “bulge”.
As long as the process works perfectly, the follicles continue to produce pigments and the hair retains its original color. As time passes, however, an ever-increasing share of these stem cells literally remains stuck in the bulge of the follicle. No longer able to reach the area where they receive the molecular signals to mature, the cells get stuck in an intermediate state, stop producing color and let the hair grow gray or white. This blockage of stem cells in the deep area of the follicle – concluded the authors of the study – is the main cause of graying, and it is therefore by attempting to restore the mobility of the stem cells of melanocytes that we could develop effective drugs and therapies against gray hair.
A more complex picture
More recently, the same team of researchers from New York University published a review on the topic of melanocyte stem cell quiescence in the journal npj Regenerative Medicinewhich takes stock of the most recent results that have emerged in this field. The new study reveals that simply physically blocking stem cells is not the only biological mechanism responsible for human hair color loss.
In fact, researchers have discovered that other factors such as the deficiency of specific regulatory proteins, environmental oxidative stress, natural mechanisms of senescence and changes that can occur within the follicles all play a key role in accelerating the entry of melanocytes into a state of senescence. When these signaling pathways are disrupted, the molecular microenvironment of the follicle loses the ability to support melanocyte differentiation, adding a further layer of chemical complexity to the graying phenomenon.
In short, more complex mechanisms come into play in the human scalp than those identified in the previous study on mice. And it is therefore not certain that if we managed to unlock the stem cells of murine melanocytes and push them to differentiate again we would also have obtained an effective therapy against human gray hair.
The last word has not been said
If the loss of color linked to natural biological aging remains irreversible for now, there is however good news for cases in which gray hair appears due to stressful events. A study by Columbia University, published in the journal eLifehas shown that pigment loss induced by psychological stress can be temporary and even reversible.
Developing a very high-resolution method capable of digitizing pigmentation patterns along the length of a single hair – much like growth rings in tree trunks – the researchers tracked the color changes in relation to the stress diaries kept by the participants.
The data has shown that during periods of strong psychological pressure or tension, the hair begins to lose color at the root. In several subjects, reducing stress or spending a period of relaxation (such as a holiday) led to the restoration of natural pigmentation. The phenomenon is linked to temporary changes in the metabolism of mitochondrial proteins within the follicle, and confirms that, at least when it comes to stress, the fate of gray hair is not always written in stone.