Premature greying of the hair is the loss of pigment within hair follicles that occurs during normal ageing. Human hair contains black to brown eumelanin and reddish-brown pheomelanin pigments. The ratio of these pigments defines the colour of the hair. During aging, the pigmentary unit which is attached to the base of each hair follicle can become modified and there is a gradual loss of melanocytes, the cells that create the pigment. The genetics that control hair pigmentation are complex, but clearly there is a genetic element. However, there is also an environmental consideration, and this suggests that the loss of pigmentation in hair is due to gradual oxidative damage to the pigmentary unit. Both the hydroxylation of tyrosine and oxidation of dihydroxyphenylalanine to melanin, two steps in the process of pigment formation, produce hydrogen peroxide as a by product, and this may significantly increase the oxidative stress in the cell, causing damage, deterioration and a loss of pigmentation.
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