Human hair greying is linked to a specific depletion of hair follicle melanocytes affecting both the bulb and the outer root sheath

Abstract

Thus, hair greying appears to be a consequence of an overall and specific depletion of bulb and ORS melanocytes of human hair.

La vie révélée du follicule de cheveu humain

“…En fait, le processus de blanchissement est dû à une décroissance progressive du nombre des mélanocytes, tant au niveau de l'unité de pigmentation que du réservoir [35]. Lorsque le nombre de mélanocytes actifs atteint un seuil limite, la quantité de mélanine synthétisée et transférée à la tige pilaire en croissance n'est plus suffisante pour que le cheveu soit perçu pigmenté, il est donc perçu blanc ; à terme, les mélanocytes disparaissent totalement de l'unité de pigmentation et du réservoir.…”

Premature Greying of Hair (Premature Canities): A Concern for Parent and Child

“…The tyrosinase enzyme is necessary for the initial stages of melanin synthesis. The hair bulb tyrosinase activity gradually peaks at middle age and the bulbs of grey or white hairs appear to lack or be deficient in tyrosinase [8]. Repetitive oxidative stress causes apoptosis of hair follicle melanocytes, resulting in normal hair greying and premature greying is related to exhaustion and poor sustenance of the melanocyte stem cell pool [9].…”

Melanin and Its Role in Hyper-Pigmentation – Current Knowledge and Future Trends in Research

“…This o-quinone is transformed into melanins in a series of non-enzymatic reactions (Baurin et al, 2002;Wang et al, 2006). There are two types of melanin pigments that can be produced by the melanocytes cells namely: 'eumelanin' (black or brown) and 'pheomelanin' (red or yellow) (figure 2.3) (Commo et al, 2004;Summers, 2006). The color of hair, skin etc in human is determined by the type, distribution and degree of melanin pigment synthesized.…”

“…Each individual of different racial group have more or less the same number of melanocytes cells, thus the type of melanin produced depends on the functioning of the melanocytes e.g. people with darker skin are just genetically programmed to constantly produce higher levels of melanin even without exposure to UV light and the melanosomes remains singular (figure 2.4) (Commo et al, 2004;Baurin et al, 2002;Kim and Uyama, 2005;Summers, 2006;Sturm et al, 1998). In individuals with fair or lighter skin colour, melanosomes cluster in membrane bound organelles (figure 2.4) (Sturm et al, 1998).…”