ABSTRACT
Human skin color is determined by the total quantity of melanin, the proportion between the brown-black eumelanin and the yellow-red pheomelanin, and its distribution through the epidermis. Melanocytes contain a unique intracytoplasmic organelle, the melanosome, which is the site of melanin synthesis and deposition. As melanin is deposited within melanosomes, they migrate along microtubules from the cell body into dendrites in preparation for transfer to keratinocytes. Racial and ethnic differences in skin color are related to the number, size, shape, distribution, and degradation of melanosomes. The understanding of the genetic mechanisms underlying human skin color variation is still incomplete; however, genetic studies have discovered a number of genes that affect human skin color in specific populations, and shown that this happens independently of other physical features, such as eye and hair color. Multiple studies have used reflectance spectroscopy for objective measurement of skin color. Highly pigmented skin prevents ultraviolet radiation (UVR)-induced vitamin D3 toxicity caused by oversynthesis of previtamin D3.
