ABSTRACT
Our visual appearance mostly relies on our skin and hair colour, and perceived variations between human subgroups can be ascribed to the different levels and types of pigments, namely melanins, involved. The hair colour results to a large extent from the presence or absence of melanins in the cortex of the hair fiber, melanins being end products of a complex biochemical pathway called melanogenesis, involving tyrosine as the initial substrate (see Chapter 1). This melanin production takes place in specialized cytoplasmic organelles called melanosomes produced by neural crest-derived pigment cells called melanocytes. A characteristic feature of the human hair melanocyte as compared with the epidermal melanocyte is its permanently activated state throughout the growing phase, i.e., anagen, of the follicle, probably supported by a specific regulatory network, as yet not fully understood.
