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The answer to this question has its reason in the hair cycle. Our hair goes through a cycle of growth. At the end of this cycle, the cells in the hair follicle die and have to be replenished before a new hair cycle starts, also the hair falls out eventually. See the figure from reference 1: The replenishment process is done by to two cell types: Epithelial ...


The absorption of gamma and x-ray radiation by skin is negligible, so the amount of melanin present is irrelevant. Stopping high energy photons requires a lot of mass, not a few microns of melanin.


Pheomelanin is associated with paler skin, while eumelanin predomominates in people with darker skin — this is influenced by alleles of the MC1R gene Swope and Abdel-Malek, 2018, NIH article on MC1R.


Mammals are born with blue eyes because the melanin level has not yet been established to give brown/yellow. Blue is the absence of melanin, so that eyes reflect outside light which is seen as blue. Melanocyte cells respond to light and will start to make melanin in the first few weeks after birth. Melanocyte cells have a range of activity and will produce ...

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